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KAON Factory study : KAON Factory science and experimental facilities TRIUMF-KAON Project 1990

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KADN FACTDRY STUDY KAON FACTORY SCIENCE AND EXPERIMENTAL FACILITIES EI ~~---TBHJMF U~BR~AR-V JUN 1 3 1990 DO !\jeT <:-\10VE ------ ........ - --_._---TRIUMF 4004 WESBROOK MALL VANCOUVER, B.C., CANADA V6T 2A3 KADN FACTORY STUDY KAON FACTORY SCIENCE AND EXPERIMENTAL FACILITIES TRIUMF 4004 WESBROOK MALL VANCOUVER, B.C., CANADA V6T 2A3 TABLE OF CONTENTS Executive Summary SCIENCE WORKSHOPS ....................................................... 1 Introduction ................................................................. 1 Rare Decays and CP Violation ............................................. 2 Neutrino Physics ........................................................... 11 Hadron Spectroscopy ...................................................... 13 Hyperon Physics ........................................................... 14 Nuclear Physics ............................................................ 16 Antiprotons at KAON ..................................................... 23 Experimental Program ..................................................... 25 EXPERIMENTAL FACILITIES REPORT ....... . ........................... 28 Introduction .................................... . ........................... 28 Secondary Channels ...................................................... 29 General Properties ........................................................ 32 Channel Designs .......................................................... 34 Production Cross Section and Channel Fluxes ............................. 38 Neutral Kaon Beam .......................... . ........................... 40 Muon Beams ................................. . ........................... 42 Neutrino Facility ................................. . ....................... 47 Target Areas ................................................................. 47 Introduction .............................................................. 47 Targets ................................................................... 47 Activation and Remote Handling ......................................... 49 Shielding ................................................................. 55 Primary Proton Lines ...................................................... 58 EXECUTIVE SUMMARY KAON FACTORY SCIENCE AND EXPERIMENTAL FACILITIES EXECUTIVE SUMMARY The scientific case for building the KAON Factory was described in the initial proposal in 1985 and was strongly endorsed by the NRC/NSERC Technical Panel and Review Com-mittee and many other subsequent bodies. When the KAON Factory Project Definition Study was funded, it was decided that an important part of this study should be to or-ganize a series of workshops to discuss the science and update this crucial aspect of the proposal. These workshops had three aims. First, to review and update the scientific case for the the KAON Factory to take into account developments in nuclear and particle physics which had occurred since the writing of the original proposal. Second, to delineate the experimental facilities and buildings which would be needed to take full advantage of this powerful new tool for exploring the nature of matter. Third, to engage the international scientific community in helping us to specify what are the most important questions to ask in terms of what experiments should have the highest priority and what would be needed to carry them out. With these aims in mind the workshops described in Table 1 in Section 3A were organized. Each had a specific theme, a scientific topic which was the focus of interest. Internationally recognized experts devoted their time and energy in helping us to update the scientific case and specify the experimental requirements. Four of the workshops were held overseas (two in Japan, one in Germany and one in Italy) in accordance with the third aim. The primary result of this series of workshops was to show that the scientific motivation for building the KAON Factory is now even stronger then when the proposal was first written. The original questions which the KAON Factory was intended to answer have become, if anything, even more urgent and new questions have arisen which were not apparent in 1985. The theory which describes the basic building blocks of nature, the quarks and leptons, and the forces between them is called the Standard Model. Developed over the past two decades, it received resounding experimental confirmation with the discoveries of the W and Z particles at CERN in 1983. Since that time it has been experimentally tested in ever more stringent ways and no breakdown has ever been found. Physicists believe, however, that the Standard Model must necessarily be incomplete, since it fails to explain many features of the world in which we live. For example, it does not even attempt to explain the masses of the quarks and leptons, or the reason for the existence of the three families of fundamental particles. It is most likely therefore, that the Standard Model is but a fragment of a more complete picture, which has yet to be discovered and which will explain those features of the Standard Model which are at present arbitrary. The most urgent task of subatomic physics is to discover this more complete picture or theory. It is a main motivation for building the sse, HERA and the KAON Factory. The way in which physicists conduct this search is to look for new phenomena, which cannot be explained by the Standard Model and which would give glimpses of the more complete picture. To look for new phenomena one must conduct experiments which test the Standard Model in new ways. This can be done by either going to hitherto unreachable energies, as is being done at the sse, or by carrying out experiments at more modest energies with unprecedented accuracy. This latter approach which will give information that is unique but complementary to the results of sse experiments, will be pursued at the KAON Factory. As an example, it has been known for many years that in certain decays of the kaon nature is not symmetric with regard to the direction of time. It is also known (as was first pointed out by Andrei Sakharov) that this symmetry is connected with the fact that the universe consists overwhelmingly of matter, and not of equal parts matter and antimatter. This time asymmetry therefore lies at the very root of the existence of galaxies, stars and ultimately ourselves, and yet its origin remains profoundly mysterious. It will be one of the most urgent tasks of the KAON Factory to carry out experiments to explore more fully the kaon decays in which the time asymmetry is manifest, and hopefully shed light on its origin. Such experiments cannot be carried out at the sse, and the question will have to be addressed at facilities such as KAON. A second example, this time for nuclear physics, is the use of kaons as probes of the nucleus. It has long been known that the kaon has two features which would make it uniquely valuable as a nuclear probe. Firstly it carries the strange quark, which acts as a kind of label or flag, rather like the radioactivity labelled elements used in chemistry, biology and medicine. One can, in a certain sense, follow the kaon as it enters a nucleus. Secondly, the positively charged kaon is able to penetrate deep into the nuclear interior, enabling physicists to use it to explore the arrangement and nature of the particles inside the nucleus. The aim here is to search for evidence of the quarks and gluons which are known to make up the protons and neutrons conventionally, pictured as nuclear constituents, and to look for new types of particles in the nuclear interior. All this has been known for many years but hitherto kaon beams have been too weak to adequately illuminat~ nuclear targets so the study of the nuclei using the kaon as a probe is still in its infancy. There is enormous interest, particularly in Japan and Europe, in this aspect of the KAON Factory Experimental Program. As a final example, we take the physics which can be explored with antimatter. The 11 KAON Factory would be by far the most intense source of antiprotons in the world. The European physics community, which has been at the centre of antiproton physics in recent years, is extremely enthusiastic about the prospects of being able to carry out studies with the higher energy, more intense antiproton beams which will be available at the KAON Factory. Such studies would range from using antiprotons in testing the fundamental symmetries found in nature to their use in creating extreme conditions of temperature and density inside nuclei. These examples are chosen from a long list of topics explored in depth at the workshops and summarized in Table 6, Section 3A. Based on the conclusions of the workshops, a representative set of experimental areas and beam lines were designed, the layout and properties of which are shown in Figure 1 and Tables 1 and 2 in section 3B. These designs would allow beams of kaons, pions, antiprotons and polarized protons to be utilized in carrying out a full program of experiments to exploit the unique potential offered by the KAON Factory. Initial funding considerations may preclude the construction of the full complement of facilities shown in the proposed layout. However, the main experimental hall, together with most of the high intensity pion and kaon beams within it, would cer-tainly be available for the initial experimental program. The precise nature of this program will depend on decisions made by an international panel of scientific advisors, as is usual for this type of facility, but might typically consist of the following set of experiments. • Study of Time Reversal Violation in the decay • Test of the Standard Model in the decay • Study of strange quarks in nuclei (hypernuclei) • Measurements with antiprotons of the anti-nucleon nucleon interaction • Probing the nucleus by scattering of K+ mesons • Study of systems of quarks and gluons (hadron spectroscopy) Later as funds become available to add the neutrino line, polarized protons and high energy kaons, this list could grow to encompass the full range of science which would be explored. As stated earlier, nature's fundamental constituents appear to be the quarks and the leptons with their associated neutrinos. The early experiments at the LEP machine in CERN Geneva, and the Stanford Linear Collider (SLC), indicate that only three groups 1ll of quarks and leptons exist. It is therefore known exactly how many constituents must be sought experimentally; currently the only missing ingredient is the 'top' quark. These quarks and leptons experience the forces of nature by the exchange of particles or quanta. For the electromagnetic force the exchanged particle is the massless photon (,-ray), for the Weak force, there are the massive W and Z particles, and for the Strong or Nuclear force the exchanged quantum is the massless gluon (g). In the attached figure the mass of all these particles is plotted against their charge in units of the charge on the electron. While mass is well defined for the leptons and exchanged particles, it is not so easily defined for the quarks, which cannot exist individually in the laboratory. The vertical scale then in some sense is merely "to guide the eye". This figure can also be used to indicate the number and range of facilities, either existing, approved or proposed, which are available to the international community of sub-atomic physicists. Many of them are "factories" specifically designed to produce in quantity one of the major particles. It can be seen that the KAON Factory is placed neatly within the world network. The salient properties of the facilities included in the figure can summarized as follows. 1. Sudbury Neutrino Observatory (SNO) In its final version, SNO will respond equally to each neutrino species, using the sun as a well-understood source. Although not a factory or one of the major new accelerator facilities it is included here because of its importance and its Canadian context. 2. The Meson Factories (LAMPF, PSI, TRIUMF) These machines have provided more than 10 years of intense beams of pions, made from up (u) and down (d) quarks. They also yield intense beams of muons (p.) which arise when pions decay. 3. The KAON Factory As stated the machine will be a copious producer of K-mesons which contain the strange quark(s). It is also a copious source of gluons (g), antinucleons, neutrinos, pions etc. 4. Charm Factories The new Chinese accelerator at Beijing (BEPC) and a proposed Spanish facility will be the world's intense source of charmed quarks (c) and also of tau leptons (r). 5. B-Factory There is intense competition to become the world's B-Factory from the Cornell Lab-oratory CESR and SLAC in the USA and DORIS in the DESY Laboratory in Ger-IV many. The b-quark has many interesting decays, and can shed new light on the question of time asymmetry, complementary to the experiments at KAON. 6. LEP at CERN, SLC at Stanford These machines are Z-factories. The detailed study of Z-decays checks the Standard Model with greater precision than ever before. 7. Hadron Colliders (SPS at CERN, Tevatron at FNAL) These machines currently are the only ones functioning at which the 'top' quark may be discovered. They are listed as 'top' factories, although as such they have not yet produced a single item! 8. HERA at DESY This facility is not depicted directly, but it uses intense sources of W and Z parti-cles and -y-rays to probe the quark structure down to distance scales not previously accessible. 9. The Supercolliders The Standard Model lacks one very important particle, the Higgs particle, which plays a crucial role in breaking nature's symmetry and giving different masses to the constituents and exchange quanta. Its mass is believed to be less than 1 TeV /c2 (1012eV /c2) . This mass scale sets the design goal for the SSC (Superconducting Supercollider) in the USA and the proposed LHC (Large Hadron Collider) at CERN. These large new machines can be regarded as "Higgs Factories". The coming decades should see all of these facilities playing their complementary roles in trying to answer the question as to "what lies beyond the Standard Model", or more generally "why are we here"? v ~(f) (f) o L 1 TeV/c 2 1 GeV/c 2 1 MeV/c 2 +1 LQ] "Higgs Factory" ( LHC SSC t Factory J SPS CERN TeVatron ~ Z Factory FNAL LEP SLC Z +w • I B Factory ,-_b---, DORIS CESR SLAC [:] CHARM Factory BEPC c .T +2/3 o ~ KAON Factory .p, -1/3 Meson Factories LAMPF PSI TRIUMF ee -1 Charge in units of e SCIENCE WORKSHOPS 3A: SCIENCE WORKSHOPS Introduction The possibilities opened up by construction of a Kaon Factory are both numerous and diverse, including opportunities for important measurements to be made in particle physics, nuclear physics, and atomic physics. This report can only sketch some of the highlights, emphasizing those aspects which have assumed increased importance since the original proposals for a Kaon Factory were written. It is based largely on a series of workshops which have been sponsored by the TRIUMF KAON Factory Project Definition Study, and which are listed in Table 1. (Five of these wockshops were held in locations away from TRIUMF; one in Montreal; two at KEK in Japan; one at Bad Honnef, West Germany; and one in Torino, Italy. This would not have been possible without the hard work and hospitality of our colleagues at these places.) Rather than describe the discussions held at each workshop, which overlapped in many cases, specific areas of physics will be addressed in turn. Table 1: KAON Factory PDS Workshops TOPIC LOCATION DATE Rare Kaon Decays TRIUMF November 30-and CP Violation December 3, 1988 Spin Physics TRIUMF February 15-16, 1989 Hadron Spectroscopy TRIUMF February 20-21, 1989 Joint JHP /KAON KEK, Japan April 3-4, 1989 Neutrino Physics Montreal May 14, 1989 Physics at KAON Bad Honnef, W. Germany June 1-9, 1989 Hypernuclear Physics at KAON KEK, Japan June 11-18, 1989 Spin and Symmetries TRIUMF June 30-July 2, 1989 KAON Users' TRIUMF July 10-11, 1989 Lower Energy Muon Science at Large Accelerators TRIUMF July 19-21, 1989 Intense Hadron Sources Turin, Italy October 23-25, 1989 and Antiproton Physics 1 Rare Decays and CP Violation In recent years the basic motivation for studying kaon decay processes has become, if anything, even stronger. The emphasis will continue to be on attacking many of the same issues addressed at the energy frontier of the high energy colliders, by looking for processes forbidden in the Standard Model and looking for rare processes which are sensitive to the effects of virtual, heavy particles. Especially interesting are those processes forbidden at lowest order in electroweak lowest order in electroweak interactions, but allowed at one loop level. At the KAON Factory one can envisage experiments with sufficient sensitivity to probe such processes at a level which will. critically test the Standard Model predictions, including those that depend on the CP violating phase inherent in the three generation quark mixing matrix. In fact there is every reason to believe that kaon decays will continue to be the rich and often surprising source of information that they have been at every stage of our present picture of fundamental particles and their interactions. Although the main emphasis is on looking for physics beyond the Standard Model, one can gain important information from K decay experiments on the parameters inside the Standard Model. This information can be used to make predictions of increasing accuracy for various processes, as our knowledge of the Standard Model parameters and hadronic corrections improves. The experimental measurement of the rate for these processes then becomes a more sensitive test of the Standard Model. A prime example of such a process is K -+ 7r+vv, where reliable higher order calculations can be confronted by experiment. Here the short distance contribution from charm and especially top quarks provides the dominant contribution to the amplitude: long distance effects are estimated to be negligible. The QCD corrections are not large, and the predicted branching ratio for K+ -+ 7r+vv, is shown in Fig. 1, with the dashed lines representing upper and lower bounds without QCD corrections and the solid lines give the correspond-ing bounds with those corrections. For a given value of the mass of the top quark mt, the difference between these bounds represents the uncertainty in our knowledge of the Kobayashi-Maskawa parameters (particularly l'td). It is interesting to note that here, as in other rare kaon decays, the contributions from the top quarks become the dominant ones when m~ » M;. The 'best' estimate of mt has risen steadily since our original proposal and now is expected to be between 60 and 200 GeV. To quote Gilman[l], "In the Standard Model, as mt rises further and further above M w , more and more one loop K physics is top physics, and we are in the interesting situation where those working at the highest energy hadron colliders are pursuing another aspect of the same physics as those working on the rarest of K decays at low energy". As may be seen in Fig. 1, the branching ratio ranges between 0.2 and 2 X 1010 per neutrino flavor. Since we now know there are only three generations, then a measurement significantly constrains the K - M parameters and mt, allowing a direct test of higher order weak corrections. 2 __ 3 r----.----.---~----~--~----~ o ..-. o ..--------------------------------------------------m O~--~----L----L--~L_ __ ~ __ ~ 50 100 150 200 6-89 m t (GeV) 6380AI Figure 1: The maximum and minimum of the branching ratio (per neutrino flavor) for K± -+ 7r±VV without (dashed curve) and with (solid curve) QCD corrections (AQCD = 150 MeV). From Ref.[1} Experimentally, the major development since the proposal was submitted has been the improvement in the experimental upper limit from 1.4 X 10-7 to 3 X 10-8 as a result of an experiment now in progress at the Brookhaven National Laboratory. This experiment (E787) is continuing and further progress can be expected, but present indications are that the experiment may be limited by the available flux of kaons rather than by background processes for the region of phase space (above the K1r~ peak) being examined. If the standard model is correct, then at most a few events can be expected from the Brookhaven experiment. The intensity available from a Kaon Factory will be needed to continue the search if the process is not seen, to investigate any new phenomena which show up, or to examine the pion spectrum and compare it with expectations (Fig. 2) if the process occurs at a rate consistent with the Standard Model. The pion spectrum is sensitive to neutrino masses, as indicated in Fig. 2. To take advantage of the intensity from a Kaon Factory means building a detector which can handle a flux one or two orders of magnitude greater than presently available. How such a detector might look is shown in Fig. 3. The major improvements over the present detector at Brookhaven are: 1. Improvement of the photon veto efficiency by the use of a fully active detection material such as BaF 2 or Cal. 2. Much greater segmentation by utilizing scintillating fibres. 3 .. 10 9 7 J.JU:.. C dE 6 .. 2 , , I I I , I , , I I l 0.20 025 ~(GeV) Figure 2: Pion energy spectrum for K+ --+ 7l"+vv with the assumption of (a) massless neutrinos (- - -), and (b) one neutrino with mass 50 MeV / c2 (-) 4 IRON RETURN YOKE ~moo§§~~~~~~ DRIFT CHAMBER , L-~~~===U~~~----~~L----RANGE ~~~~==~~~~----~~r----STACK ~~~~~~~~/ Apparatus for the K + nvv search PHOTON VETO __ ~=-~~~~~RANGE STACK DRIFT CHAMBER Figure 3: Apparatus for the K --+ 7rVV search and cross sectional view of the apparatus 5 3. Better momentum resolution and smaller size with the use of a higher field super-conducting solenoid. 4. Improved instrumentation on all channels using 1 GHz transient digitizers or GaAs CCD's being developed at TRIUMF. A sensitivity of < 4 x 10-12 should be achievable with negligible background. If the branching ratio turns out to be 5 X 1010, several hundred events would be observed, enabling the 71"+ momentum spectrum to be determined in addition to the branching ratio. Turning to rare kaon decays which are absolutely forbidden by the Standard Model, let us consider lepton flavour violating processes such as K2 -+ p.e and K -+ 71"+ p.+e-. Manyex-tensions to the Standard Model allow flavour violations, which are mediated by horizontal gauge bosons, additional neutral Higgs, lepto quarks, or supersymmetric particles. (See Fig. 4, which shows possible contributions to K2 -+ p.e, for example.) The mass regions probed by rare decay processes can be estimated from the formula[2] [10-12 ]4 MH ~ 200TeV B.R. (gH/gW) where B.R. is the branching ratio for the decay process mediated by a particle of mass mH and coupling 9H. With rare decay sensitivities of order 10-12 , the mass regions probed are obviously inaccessible by direct experiments at high energy colliders. The experimental situation has changed significantly as a result of recent experiments at Brookhaven and KEK and is summarized in Table 2. Further progress can be expected and it appears realistic to anticipate sensitivities of ~ 10-13 could be achieved at a kaon factory with higher intensity beams. Although the experimental problems will be formidable, it is worth remembering that whereas the meson factories provided two orders of magnitude improvement in flux over their predecessors, this, coupled with detector improvements, has already led to five orders of magnitude improvement in sensitivity of rare muon decay experiments, and major advances are still underway. Turning to CP violation, the most dramatic development since the proposal has been the apparent observation [3] of a non-zero value of f.'/f at CERN of (3.1 ± 1.1 x 103 ), consistent with the Standard Model. A Fermilab experiment (E731) of comparable pre-cision is rumoured to give a result inconsistent with this. The statistical accuracy of these experiments is limited by the size of the K2 -+ 271"° sample, which is typically a few hundred thousand. An order of magnitude improvement to the 10-4 level would require '" 108 K2 -+ 271"° events, necessitating much higher kaon flux, much improved detectors, and better understanding of systematic errors. There is much current interest (both theoretical and experimental) in studying the decay K2 -+ 7I"°e+ e- , which has the unusual feature that it can proceed over both CP conserving 6 (a) s d ~ I ~ (b) IH I I e e s I ~ (c) Ip I ~ I d fL S WL e (d) u~c.tDv d WR fL Figure 4: Contribution to K2 -+ p,e from (a) horizontal boson E exchange, (b) Higgs exchange, (c) leptoquark exchange, (d) W R exchange 7 Table 2: Mass Bounds from Different Processes Higgs Pseudoscalar Vector Experimental Process scalars leptoquarks leptoquarks Value (GeV /c2 ) (TeV /c2 ) (TeV /c2 ) r(Kk ..... l-'e) r(K L ..... all) 11 8 149 < 3 x 10+10 (a) r(~ ..... I-''ii) r( L ..... all) 4.7 3.6 62 9 x 10-9 (a) r(K~ ..... ee) r(KL ..... all) 8 2.6 108 < 1.2 X 10-9 (c) r(K+ ..... 7r+l-'e} 1 0.5 5.6 < 1.8 X 10-9 (d) r(K+ ..... all) r(1-' ..... e-y} 0.3 < 4.9 X 10-11 (e) r(1-' ..... all) r(1-' ..... eee} 2.6 < 1.0 X 10-12 (f) r(1-' ..... all) r(l-'z ..... e:A} 22 22 118 < 4.6 x 10-12 (g) r(1-' z ..... "Z') ~m(K2 - K~) 150 3.6 x 10-15 GeV (b) (a) W.R. Molson, Proc . Rare Decay Symposium (Vancouver, 1988) (b) Particle data group, Phys. Lett. 170B (1986) l. (c) E. Jastrzembski et al., Phys. Rev. Lett. 20 (1988) 2300 (d) M. Zeller, Proc. Rare Decay Symposium (Vancouver, 1988). (e) R.D. Bolton et al., Phys. Rev. Lett. 56 (1986) 246l. (f) U. Bellgardt, Nucl. Phys. B299 (1987) l. (g) S. Ahmad et al., Phys. Rev. 38 (1988) 2102. 8 and CP violating routes (Fig. 5). FUrthermore it seems that the CP violating components due to !::is = 2 and !::is = 1 amplitudes may be comparable. The situation is therefore complex, but potentially rich in information if sufficiently precise experiments can be done. The branching ratio is in the 10-12 to 10-11 region, so the experimental difficulties are formidable, since more than the rate alone must be measured to unravel the various contributions. New experiments are being mounted at KEK, BNL, and Fermilab, but need for significant statistics makes this reaction a natural one for the KAON Factory. FUrther (a) __ K_L __ ~~ e-(b) Figure 5: Diagrams for K2 -+ 7r°e+e-. (a) CP conserving two photon process (b) CP violating penguin diagram evidence of CP violation would be the observation of longitudinal muon polarization in K2 -+ J-LJ-L, expected to be I'V 10-3 in the Standard Model, but which could be much larger in Higgs models of CP violation. No experiment to search for this has yet been done and it appears that the intense beams at a Kaon Factory could be required to reach the 10-3 level. The Higgs model also predicts a non-negative value of the transverse muon polarization in K -+ 7rJ-LV, in contra-distinction to the Standard Model. The prediction is, however, about an order of magnitudes below the present experimental limit of 10-2 reached a number of years ago. It would probably be valuable to start a new generation of experiments using modern techniques and significant progress could be made even before the KAON Factory era. A different approach to the problem is to use pp annihilation to produce pure, tagged KO and KO states, as is being done in an experiment at LEAR, which is expected to produce values of f' / f and the associated phases with a precision comparable to the CERN and Fermilab experiments. It is particularly valuable in that it gives an independent check with quite different systematic uncertainties than at CERN and Fermilab. It may well be 9 that future developments of this experiment will require Kaon Factory intensities. Antiprotons may also be used to investigate CP violation by studying the asymmetries of hyperon polarization in the reactions pp and ppAA and pp -+ 33 as discussed by Hamann. This could be very valuable since it could provide a way to study CP violation outside the neutral K system. The hyperons are known to be produced with large polarizations of order"'" 0.5. Both initial and final stages have well defined values of CP, and baryon number conservation prevents Y - Y mixing, so that any observed signal constitutes a measure of 6S = 1 CP violation. Predictions for the CP violating asymmetries lead to effects of the order of 10-4 in experimental observables, which is one or two orders of magnitude smaller than appears measurable with current machines. The cleanest measures of CP violation is given by observing both the decay asymmetry and the final state polarization in the reaction pp -+ 33 which gives a sequence of two self-analyzing delayed decays. An event of this kind is shown schematically in Fig. 6. In the first decay, 3- or 3- -+ A7r- or A7r+, one measures the up-down asymmetry of the 3+3- decay angles distribution. In the second decay A(A) -+ p7r+, (P7r-) one measures the A, A polarizations from the asymmetries of the decay distributions. The threshold for this reaction is above 3 Ge V I c incident p momentum, which is above LEAR energies but makes it a suitable candidate for consideration of the KAON Factory. -7T A _------Figure 6: An event pp -+ 3+3- -+ A7r+ -+ p7r+ 7r+P7r-7r- generated at 3.5 GeV Ic incident p momentum 10 Neutrino Physics The basic motivations for neutrino physics at the KAON Factory remain as before: (1) tests of electroweak theory, (2) probing the structure of hadrons, (3) probing the nucleus. As far as testing electroweak theory goes, the two main areas of interest for the KAON Factory are (a) the determination of sin29w at low Q2 by the study of neutrino-electron scattering and (b) searching for neutrino oscillations. The present best values of sin29w by this technique (from CERN and BNL) have a precision of'" 10%, but the LCD experiment[4] proposed for LAMPF proposed to reduce this to '" 1%. It is unlikely that an experiment at the KAON Factory could improve on this, so the situation should be re-evaluated later to see how the LCD proposal progresses. Evidence of neutrino oscillations would be extremely important in demonstrating that neutrinos have mass, which is expected on both theoretical and cosmological grounds. There is at present no convincing evidence for oscillations, however, as can be seen in Fig. 7, which shows the present limits together with those expected from a recent proposal[5] at BNL. This proposal would use two detectors at 150 m and at 1000 m, with a later development extending the baseline to 10 Km. A Kaon Factory beam with 25 times the luminosity expected at BNL with the booster could push the limit on 6m down to the few X 1O-4ey2 level by going to a baseline of '" 100 km. This level of precision is interesting because proposals to solve the solar neutrino problem by matter oscillations require Ve -+ vI! oscillations occur with Am2 '" 10-7 to 10-4 ey2. Neutrino experiments on this scale are, however, massive in size and cost and would be done in the context of the then current results of terrestrial and solar neutrino experiments. Less ambitious is the use of neutrinos as a probe of hadron structure in which a small, smart detector would capitalize on the high flux available from a Kaon Factory probe hadron structure; for example, measurements of neutrino and anti-neutrino elastic scattering at low Q2 may be the best way to determine the strange quark content of the proton, a question of great current interest as a result of the recent EMC measurement[6] of the spin content of the proton. Measurements of quasi-elastic anti-neutrino scattering from protons VI! + P -+ 1'+ + n would provide information on the axial part of the nuclear weak form factor (the vector part being obtained from electromagnetic scattering) and could be used to look for tensor components. Measurements of production by anti-neutrinos: vI! + P -+ AO + 1'+ might make it possible to measure the Cabibbo angle, VU", as a function of Q2 . This type of experiment looks very suitable for starting a neutrino program, and might, if a suitable detector can be designed, be done in conjunction with nuclear physics investi-gations using neutrinos. The nucleus can be used as a filter to pick out specific parts of the weak interaction. As an example, the reaction 12 C 12 C +' VI! + -+ 15.11 VI! 11 "..... N ~ ~ Na <J .------CCFR ........ - . .) r--'--:;> ----.,.,.- . ...-- . ~ CDHS .. ~---------, . 10 1 ----/"-\. "- \ ./ ("CHARM 10° \ v~ disappearance Figure 7: Parameter space investigated by neutrino oscillation experiments. The square mass difference of the neutrinos is given by ~m2 and 8 is their mixing angle. The curve marked '1Ij1 disappearance' is the sensitivity of the BNL proposal 12 proceeds via the isovector axial coupling. Thus we can use nuclear physics selection rules to learn about the weak interaction. On the question of whether the KAON Factory should build a decay-in-flight neutrino facility, as described in the proposal, or a beam stop facility after the Booster, the decision may hinge on whether LAMPF goes ahead with pleas to upgrade to a 1.6 Gev facility. For the moment it seems that the decision to plan for a decay-in-flight facility of the Brookhaven type is the correct one. Hadron Spectroscopy Although we believe we have the correct theory of the strong interactions, QeD, the theory is so complicated that we cannot solve it even for a one hadron system. We must, therefore, rely on models as a framework to understand the physics. Because the quark model remains the most useful tool in understanding hadron spectroscopy, it is reasonable to divide spectroscopy into conventional quark model states and exotic gluonic and multiquark states, at least as a preliminary classification scheme. As far as conventional quark model states are concerned, many more states are predicted that have been observed. In the baryon reaction, only those states which couple strongly to the 7r N formation channel, where most experiments have been done, have been seen. One way to find the missing states is to study channels which coupled more strongly to them. Another way is to produce baryons in the trp and K p channels, some of which will be formed as decay states from higher states. High statistics experiments with the intense beams available at the KA 0 N Factory will be needed to disentangle the large number of states expected, particularly above 2 GeV. Particular emphasis may be placed on the almost unexplored sssS1 baryons. The meson sector is in much worse shape with respect to the number of confirmed quark model states. The problem is that mesons are more difficult to produce via t-channel exchange and there is little control over the flavour quantum number. In addition the states are often broad and overlapping, can and often do mix, and there is the possibility of exotic gluonic and multi-quark states in the spectrum. To sort all this out will require the very high statistics that only the KAON Factory can give. Turning to the question of exotic states it seems that our best chance of seeing such objects is in the meson sector, because there are no hybrid baryons with exotic quantum numbers (due to the greater number of degrees of freedom of the three quark states). In the meson sector the main impediment to finding exotic states with conventional quantum numbers is our incomplete understanding of the conventional mesons. It is, therefore, possible that we have seen exotics but do not realize it or cannot prove it. To recognize unambiguously such states will require a much better understanding of conventional mesons than we 13 have at present. Fortunately, in the meson section, exotic", are predicted with quantum numbers which are inconsistent with the quark model. The discovery of such states would be unambiguous proof of new forms of hadronic matter, a major event that, of its own, would justify the construction of the KAON Factory. Hyperon Physics The possibility of producing useful beams of hyperons at the KAON Factory will make feasible greatly improved measurements of hyperon beta decay parameters. Such mea-surements have an important bearing on three fundamental problems, all related to SU(3) (flavour) symmetry-breaking. 1. The testing of the unitarity of the Kobayashi-Maskawa matrix, which is based on the number of quark-lepton generations, is already significantly limited by our incomplete understanding of hyperon beta-decay. We need to improve our knowledge of the decay rate and axial vector/vector ratios by an order of magnitude to demonstrate that we understand SU(3) (flavour) symmetry breaking. 2. Polarization measurements of deep inelastic scattering on protons[6] have recently suggested that the net polarization of the valence quarks is surprisingly small. How-ever, the derivation of this result, which has sparked intense interest both theoret-ically and experimentally, is significantly sensitive to the numerical value of F /D, which emerges from the study of hadronic, beta decay. A much better value for ' this quantity is needed to have confidence in the analysis of the deep inelastic data. 3. Sizeable Second Class Current terms are expected in hyperon beta-decay, arising from the SU(3) symmetry breaking. It is important to confirm this before we can claim a satisfactory understanding of the baryon octet. The only checks which can be applied to the adequacy of theoretical estimates of SU(3) symmetry breaking effects are the agreement between theory and experiment in the case of the magnetic moments of the hyperons and the adequate convergence of the hyperon beta-decay parameters, i.e. the crossing at a point within errors of the bands in Fig. 8. As can be seen from the figure present accuracy on the better determined hyperon decays is at the level of several per cent (as against tenths of a per cent for neutron decay). It does not seem impossible to improve the situation by the required order of magnitude with the intense fluxes of hyperons which will be available at the KAON Factory. Improved measurements of the hyperon magnetic moments would also be most valuable. Hyperon beams will also enable study of hyperon-nucleon scattering, a topic of great in-terest for QCD. At the simplest level, it would be very instructive to be able to compare 14 LL o LL 0.4 0.2 0.0 ~"""'---''-----'-----L.-_--L_....3I...-.J 0.3 0.5 0.7 0 .9 u 1.3 o Figure 8: Internal consistency of beta-decay within the lowest baryon octet following the expectation of the Cabibbo scheme in the F /D parametrization. The upper figure is derived from the lifetimes using sinBc = 0.22; the lower figure is derived from the axial-vector/vector ratios. The stippled bands indicate the experimental errors. (No cor-rection has been applied for SU(3) symmetry-breaking.) 15 and contrast hyperon-nucleon scattering with nucleon-nucleon scattering which is now rea-sonably well understood in terms of meson exchange potential models such as the Bonn potential. Attempts have been made to extend this type of approach to hyperon-nucleon scattering, but experimental data are so sparse that it is impossible to say whether present ideas are correct. Most of the world's data was obtained in the 1960's with bubble cham-bers. It would be very valuable to have more data, particularly polarization data in the region below 1 GeV, not only because the topic is of substantial intrinsic interest, but also because the present situation leads to unstable theoretical predictions in theoretical models of hyper-nuclei. Nuclear Physics The basic aim of the nuclear physics program at the KAON Factory will be to shed light on non-perturbative QCD and its relation to conventional nuclear physics. If we look back in the history of nuclear physics we see that the 1950's and 1960's were dominated by the interplay between the collective model and the shell model of the nucleons, in other words between the role of nuclear matter and nucleons in the nucleus. The 1970's and 1980's saw the issue of mesonic exchange currents and 'non-nucleon' exotic particles in nuclei emerge, with the role of 7r'S and ~'s as nuclear constituents. Now and in the near future we see the question of the role of quarks in nuclei come to the forefront, i.e. what are the relevant degrees of freedom in nuclei? Can we continue to think of nuclei as made up of protons and neutrons (with a few 7r'S and ~'s thrown in) or are these nuclear phenomena which will force us to take the underlying quarks and gluons into account explicitly? Let us first consider kaon scattering and specifically the K+ -nucleon scattering and inter-action, and K+ -nucleus scattering. There is, of course, a major difference between the K+ -N and K- -N interactions; the former is much weaker than the latter because of the impossibility of forming S-channel qqq resonances from K+ (Fig. 9). Resonances in K+N would necessarily involve five quarks (Z *) and the existence of such objects is still con-troversial. We need better K-N data in the 1-2 GeV Ic region to resolve this controversy. This points up the fact that the K-N data base is still poor. There are ambiguities in the phase shifts, polarization data are scarce (no K -n data for p < 1 Ge V I c) and there is no spin rotation data at all. Figs. lOa and lOb show three different phase shift solutions, together with the available cross section and polarization data at 500 MeV. As you can see the data are quite unable to discriminate between the possible solutions. If we examine the spin rotation parameters Q, however, (Fig. 10c) we see large differences among the three solutions which could easily be resolved in less than one day of running at the KAON Factory. It is important to improve our knowledge of the K+ -N interaction, not just for its own sake, but also because doing so will enable us to use the K+ as a probe of nuclei. The lack of resonances in the K+ N interaction means that the low energy K+ has a very long mean free path in nuclear matter, longer than any other hadron (Fig. 11). The K+ can, therefore, be looked upon as a 'heavy electron', with the following list of advantages as a nuclear probe: 16 S=-1 S=+1 + K u y u Figure 9: The K- N and K+ N systems • It is weakly interacting so it can reach the nuclear interior. • It has no known resonances (such as 7rN -+ ~). • Inelastic channels are not open or negligible. • There is no annihilation channel. • There is no particle identity problem (such as in N-Nucleon) leading to there being no exchange interaction. • The tp approximation should be good and estimates of V ~:: reliable. • Medium modifications are absent (unlike N -nucleus). • High momentum transfer is possible with K N still elastic. • The cross section return K+n/ K+p goes through unity at p = 500 MeV, enabling one to change the sensitivity to neutrons or protons by varying the momentum. As an example, consider the application of the K+ probe to an old problem in nuclear physics, the derivation of neutron densities in nuclei. Proton densities as determined by electron scattering do not agree with the best Hartree-Fock calculations at the centre of heavy nuclei[7], while there are no reliable determinations of neutron densities in spite of many years of effort using intermediate energy protons and particles. A recent paper[8] comparing the sensitivities of K+ and protons reached the conclusion that K+ are about equal to protons at the surface and five times better in the nuclear interior. This is 17 ( a) (b) (c) -t;; I. I ......... ..0 1.0 E '-' 0.9 ~ "0 0.8 ......... b 0.7 "0 + K - P 502 MeV -- SOL.I - - -- SOL. 2 _. - SOL.3 10 20 30 40 50 60 70 8cm (deg) I. a r----r--r----.---.----.---r-----r.::--..---.---. 0.8 0... 0.6 0.4 0.2 + K - P 506 MeV -- SOL.I ---·SOL.2 -·-SOL.3 10 20 I. a r----r---.--r---r.....:....;.;..,..--r---, 0.8 0.6 0.4 0.2 + K - P 500 MeV ---..... - -........ .".,. ....... '1 a 0.0 r==========----i -0.2 -0.4 -0.6 -0.8 30 40 50 60 70 80 90 8cm (deg) Figure 10: Three allowed phase shift solutions for K+ P and measured values of (a) the differential cross section (;~), (b) the analysing power (P), and (c) the value of Q = 2Re (d!iln). Also shown is the estimated measurement error attainable in less than one day of running at the KA 0 N Factory 18 7r----r--------.--------,--------~ 5 E 200 400 600 800 ~AB (MeV/c) Figure 11: Mean free path (A) of various hadrons III nuclear matter as a function of momentum (PLAB ) obviously a consequence of the long K+ mean free path in nuclear matter. Figure 12 shows the effect on the ratio of the differential elastic cross sections of 160 to 180 for 50 MeV K+ of changing the neutron density radius of 160 by 10%. It is clear that K+ elastic scattering at the larger angles will be an extremely sensitive way to measure neutron densities. Most of the problems associated with nucleon-nucleus scattering either d,o not exist or are much reduced for the K+. A logical approach to utilizing its desirable properties is outlined in Table 3, where one starts by delineating the low energy K-N phase shifts, tests one's understanding on deuterons and (A=Z) nuclei (where neutron distributions are presumably known) before attaching the more difficult general case. One could then attack the neutron transition densities using inelastic scattering. Finally, two other reactions would be of great interest. The first is the use of the (K+ ,p) reaction to search for narrow S = + 1 states (so-called hypernuclei). The second is nucleon knockout, A(K+ ,K+N) where the long mean free path of the kaon should enable one to access deeply bound shell model hole states, particularly neutron states, which are probably not accessible in any other way. All of this has been known for many years and one might ask why so little progress has been made. The answer is that the inadequate K+ beam intensities available in the past have meant low count rates, thick targets , poor energy resolution and poor statistical accuracy. All this would change with the advent of the KAON Factory, which would revolutionize this type of study. 19 1.3 50 MeV 0 (X) 1.2 "-0 CD 1.1 0 ~ 1.0 <{ a::: 0.9 ........... ---0.8 30 60 90 120 150 Bern Figure 12: Ratio of differential elastic cross sections of 160 to 180 for K+ at 50 MeV. The solid line represents a standard set of parameters; the dashed line has a 10% change in the neutron density radius of 180 Table 3: A Possible K+ Experimental Program System Measure uPQ uP(Q) N = ZA(K+ K+) . t elcuttc 20 Remarks Use d-(lHf) target quasi free Test of "exact" calculations Test reaction mechanism Deduce neutron distributions Deduce neutron transition densities, collective 2t, 31 surface peaked 2t peaked in interior In the field of hypernuclear physics there are many open questions, including: • The nature of the hyperon-nucleus potential and its relation to the hyperon-nucleon interaction • The impact of the Pauli Exclusion Principle and the nature of deconfinement • The behaviour of the s-quark in the nuclear environment • The weak decay of the nucleus through the process A + N -+ N + N • The status of ~ hypernuclei • The existence and properties of doubly strange hypernuclei • The effects of the hyperon on the macroscopic properties of the host nucleus such as its radius, magnetic moment, etc. Two basic reactions have been used to investigate hypernuclei, the (K-, 7r-) reaction and the (7r+ , K+) reaction. The characteristic features of each are summarized in Table 4. (K-,7r-) studies have been confined to light nuclei, whereas (7r+, K+) has been used up to 209Bi[9] . Only low-lying states have been observed, with energy resolutions typically 3-5 MeV, utilizing small acceptance spectrometers. Elementary Cross Sections Beam Intensity (Purity) KAON m.f.p Momentum Transfer Physics Table 4: Hypernuclear Physics - Techniques 2,500 105- 6 (1:1) 1-2 fm small Mainly probes "substitutional" states near the Fermi surface 500 108- 9 very high 5fm large Preferentially excites high spin deeply bound states, can produce spin polarised hypernuclei From 1990 onwards the new KEK experimental hall, with its new beam lines and super-conducting spectrometers, will open up a new era in this field, with energy resolutions 21 approaching 1 Mev and very large acceptance spectrometers. We would expect that the KAON Factory era, beginning hopefully around 1995, will lead to even greater progress, with higher quality, more intense beams and developments in instrumentation giving en-ergy resolutions of at most a few hundred keY. Higher intensities will also make coincidence measurements much easier, enabling us to study the decay of hypernuclei. For example, it has recently been suggested[10] that both the (11'"+, K+) and (K-, 11'"-) reactions, with incident beam energy of order 1 Ge V I c, can produce spin orientated hypernuclei in which the intrinsic spin of the A is also well polar-ized. If this turns out to be true, and an approved experiment at KEK will soon test these ideas, then angular correlation studies of -y-rays and weak decay particles from polarized hypernuclear states may open up a new field of hypernuclear spectroscopy. Information on electromagnetic moments or weak decay mechanisms might be obtained in this way. The higher beam intensities available from the KAON Factory will also be essential for producing doubly strange hypernuclei via the (K-, K+) reaction. Only a few events of this type have ever been seen, all in emulsions, because of the extremely low cross sec-tions involved. Such experiments can give vital information on AA and = N interactions. Experiments to search for the doubly strange H-dibaryon, predicted to be a bound state because of its high degree of symmetry, are also intensity limited. One such search has just completed data-taking at KEK (E176) and results are expected soon. Another is about to start at BNL (E813). Even if the H is found in these experiments, detailed study of its properties must await higher beam intensities. For instance, it has been suggested that the H is large in physical size, because it is weakly bound. Study of its production rate as a function of atomic number, A, might give information on its transmission through nuclear matter, which would be very interesting. Turning to the subject of spin physics at intermediate energies, large and unexpected effects have been seen. For instance, the structure in !:J.UL and !:J.UT in p - p elastic scattering first seen at the ZGS have been interpreted as evidence for dibaryons, although the subject is still clouded by controversy. The high degree of polarization seen as inclusive A production at several laboratories is not at all understood. Finally, the structures seen in both Ay and Ayy in high Pi elastic proton-proton scattering (Fig. 13 (b)) still defy explanation. The difficulty is that perturbative QCD predicts that all such polarization effects should be zero. This kind of experiment may, therefore, teach us about constituent wave functions and parton dynamics on the region between Perturbative QCD and confinement. We should, therefore, push to the highest possible pi in the hope of seeing the onset of Perturbative QCD behaviour in spin observables. Cross sections are, however, falling rapidly (5 or 6 orders of magnitude between 10 GeV Ic incident energy and 30 GeV Ic, at around 90° in the cms) (Fig. 13 (a)). Thus beam intensity may again become an important factor. At present the AGS has 1.5 nanoamps of polarized protons up to 18.5 GeV Ic, and the upgrade should boost this to 30 nanoamps. TRIUMF now accelerates about 1 J.l amp with 70% polarization and we are commissioning a source to give several J.l amps. The 22 KAON Factory is being designed to accelerate all of its beam to 30 Gev/c with little polarization loss « 15% estimated). It will be necessary also to develop polarized targets able to withstand higher beam intensities, and to investigate the feasibility of using gas jet internal targets. Anti-Protons at KAON Present plans for the experimental facilities available at KAON do not include a 15 accumu-lator or storage ring, at least initially. Nevertheless KAON could deliver antiproton beams with intensities in the range of 106 to 108 per second at momenta between 500 Mevlc and several GeV Ic. These intensities would be quite competitive with other antiproton facilities such as LEAR, except at momenta below 500 MeV Ic. In particular, the energy regime above the maximum LEAR energy of 2 Ge V I c is relatively unexplored. It appears that a rich and varied program of physics could be carried out with antiprotons at KAON. With low energy antiprotons meson spectroscopy could be explored, searching for the missing states, exotics, glue balls, and hybrids described earlier. At higher energies, charmonium may advantageously be studied in the 15P system, which is not restricted to 1- states as is the e+ e- system. Also of great interest is the anti nucleon-nucleon force, not only in its own right but also as input for p-.nucleus calculations. The N N system differs from the NN because of the annihilation channel and the different effects of meson exchange terms. To perform the necessary amplitude analysis will require measurement of spin parameters as well as cross sections in both 15P and Tip systems. Much of this is currently being done at LEAR but it will be necessary to extend the work to higher energies. Antiprotons of several GeV in energy have also been suggested as an interesting probe of nuclear dynamics, in that the projectile can deposit a large amount of energy in a small volume of a heavy nucleus. The reaction is characterized by producing a high temperature, comparatively low density region, in contrast to relativistic heavy ion reactions resulting in both high temperature and high density. Finally, antiprotons and other negatively charged hadrons such as K-, E-, and =- can produce exotic atoms which can be used to study properties of the hadrons and the effects of the strong interaction on energy levels. Such experiments can most advantageously be carried out at a Kaon Factory, where very high intensity stopping kaon and hyperon beams will be available. A summary of the anti nucleon physics which appears to be of most interest is listed in Table 5. 23 10-30 090° 10-31 • 80° -N pp-.,pp > 10-32 Q.) (9 ......... (a) N ' 10-33 E u .......... -"'0 10-34 ......... b dcr/dtxO.l "'0 10-35 10-36 10 20 31 ~AB (GeV) 7 P+P-+P+P 6 0 5 ~ o 90cm 4 • 11.75GeV/c Q) §l j' e 3 Q) ~ a e a.. \ I (b) ~ .- \ I 0 c: 2 q fI a.. a b b \ \ \ I •• ~~o=-0 _____ ~I .... . .. • o 2 3 4 5 6 2 2 FJ.. (GeV/c) Figure 13: (a) The large angle P - P elastic scattering differential cross section as a function of incident momentum. (b) The ratio of spin parallel to spin anti parallel differential cross section as a function of Pi for p - p elastic cross section. Open circles represent 900 measurements at various energies; dots represent measurements at various angles up to 900 at 11.75 GeV Ic 24 Table 5: Anti-Nucleon Physics Meson Spectroscopy • Missing states • Exotics • Glueballs • Heavy quarks N - N Interactions • Annihilation potential • Meson exchanges • S-channel resonances (baryonium) • Phase shift analysis • Polarised p n d N-Nucleus • Pi Multiplicity • Unusual annihilations • New states of matter • Nucleus at a Q.M. filter • Ko suppression • A excess • d-nucleus Fundamental Interactions • Gravity • CP Experimental Program An experimental program which might take place at the KAON Factory is summarized in Table 6, together with the beams required to carry out such a program. Based on these considerations, the experimental facilities described in Section 3B have been developed. The experimental facilities which will eventually be built may differ from those described depending on what experiments are approved by the program advisory committee and on considerations of cost, etc, but the proposed layout serves to give the scale of what will be required to exploit properly the rich opportunities opened up by construction of the KAON Factory. Future possibilities, such as a later energy increase to 100 GeV at reduced current must also be allowed for. The aim must be to retain the maximum flexibility while satisfying the greatest number of users in the most economical way. 25 Table 6: Physics Opportunities and Requirements Rare Decays CP Violation Neutrino Physics Meson Spectroscopy Baryon Spectroscopy Kaon-Nucleon Scattering Kaon-Nuclear Reactions Hypernuclei Spin Physics Antiproton Physics Low Energy Muon Physics 26 KG, stopping K+ few GeV Ic KG 1-2 GeV neutrinos beam stop neutrinos? 8-15 GeV Ic K± up to 20 GeV Ic 1\"± 0.5-2.5 GeV Ic 1\"± 1-6 GeV/c K± 0.3-2.5 GeV Ic K± 0.3-1.0 GeV Ic K± 0.3- 2.5 GeV Ie K± 1.0-1.5 GeV Ic 1\"± 3-30 GeV/c p 0.5- 10.0 GeV Ic p Low energy JL± References [1) F.J. Gilman, SLAC Preprint SLAC-PUB-4992 (1989). [2) See, for example, R.N. Calm and H. Harari. Nucl. Phys. B176 (1980) 135. [3) H. Burkhardt et al., Phys. Lett. B206 (1988) 169. [4) R.C. Allan et al., Los Alamos Proposal, LA-11300-P (1988). [5] J.J. Lee et al., Brookhaven Proposal 848. [6] J. Ashman et al., Phys. Lett. B206 (1988) 364. [7] B. Frois, Lecture Notes in Physics 108. [8) W.R. Coker, J.D. Lumpe, and L. Ray, Phys. Rev. C31 (1985) 1412. [9] P.H. Pile et al., 1988 International Symposium on Hypernuclear and Low Energy Kaon Physics (Legnaro, 1988). [10] H. Ejiri, T. Kishimoto, and H. Noumi, Osaka University Preprint OULINS 88-12. H. Bando, T. Motoba, M. Sutona, and J. Zofka, Phys. Rev. C39 (1989) 587. 27 EXPERIMENTAL FACILITIES REPORT 3B: EXPERIMENTAL FACILITIES REPORT Introduction The successful operation of an accelerator laboratory is based not only on the performance of the machine but equally on the provision of adequate space and facilities to carry out the experimental program defined by the scientists using it. T he design of the experimental areas and the facilities servicing them are therefore of critical importance to the overall laboratory design. The beam switchyard and experimental areas for KAON, as developed during the PDS, are described below. They are intended to address, at least in part, the expected scientific program as developed in the series of workshops conducted during this study. The proposed layout represents only one choice in a multitude of possibilities which could encompass the broad range of physics opportunities available at an intense hadron facility. These experimental areas are not intended to be definitive as the initial experimental program will not be fixed until specific physics proposals have been reviewed and approved. They do, however, set the scale and costs ofthe facilities required to exploit the proposed accelerators and address many of the problems to be faced in developing these facilities. The physics workshops conducted during the past year have indicated requirements for a broad range of secondary beams. The exact properties of the beams in terms of momentum, particle type, intensity, purity, resolution etc. were highly dependent on the particular experiment discussed. It has been assumed for the purposes of this study that a set of charged secondary channels spanning the full momentum range available at KAON will be required. The channels as proposed will include particle separation to provide the purest possible beams of pions, kaons and antiprotons. In addition to these channels it is clear that a full physics program at KAON will also require at least one neutral kaon channel, a neutrino facility, a number of low energy pion or II .. llon channels and a polarized proton beam. All of these have been included in the present layout of the experimental areas. A major design requirement for the experimental areas is the maintenance of maximum flexibility to respond to changing physics requirements. Some possibilities identified during the PDS have not been included in the experimental layout. These include such facilities as an antiproton accumulator, internal polarized targets, pion therapy facilities, a beams top neutrino source, time-separated antiproton beams, 3 GeV Ic facilities etc. These have not been explicitly included due to their cost, their lack of uniqueness to KAON or to presently preceived interest. However, wherever possible, provision has been to accommodate such facilities with a minimum of disruption. Future expansion and development of the beam-line facilities must also be anticipated. Sufficient unencumbered space has therefore been provided in the present plan to accommodate a second experimental hall if and when this is required. 28 One problem which must resolved within the experimental areas is the dissipation of the 3 MW of beam power being delivered by the accelerators. The production targets, down-stream elements and beam dumps must be capable of absorbing high power densities. These components will have to be heavily shielded to protect both personnel and exper-iments from the high radiation fields produced during beam operation. Air activation is expected to be a significant problem which implies that the shield must be contained in an airtight enclosure. All components in the target areas will have to be radiation hard and residual radiation fields will make the remote handling of these components manda-tory. Conceptual approaches to these problems have been developed during this study which give confidence that they can be successfully resolved. However, detailed designs and prototypes remain to be done. The 30 Ge V beam from the accelerator can be provided as a single 3.5 p.s pulse from the Driver ring or as a quasi continuous beam from the Extender ring with or without rf mi-crostructure. In the present design the fast extracted beam from the Driver will be required for the neutrino facility. The slow extracted beam from the Extender will have to be split to service two or more production target areas. The extraction and splitting processes are of particular concern in the facility design as these processes tend to be inefficient and produce beam loss. A design has been developed which, according to calculations, should allow the extraction and continuous splitting of the beam with very small beam losses. This has been incorporated in the present facility layout. Some beam losses must be anticipated in these processes and therefore these regions are covered by an extraction building which will provide removable shielding and vertical access via an overhead crane. Experimental Hall The proposed layout of the primary and secondary beam lines is shown in Fig. 1. In this layout, six charged secondary channels are provided which view three production targets and taken together span the momentum range from 0.4 to 20 GeV Ie. A neutral kaon line is taken from a fourth production target. Provision has been made, where possible, for the extraction of low energy pion and muon beams in the backward direction from the production targets. One such channel could be used for pion therapy. The four produc-tion targets are arranged with two in line targets serviced by one of two slow extracted proton beams. These beams are sufficiently separated that the pairs of target stations can be operated and serviced independently. All production targets and beamdumps have been located in a single large (70 m X 185 m) experimental hall (Fig. 2) and can be accessed by a common overhead crane. This allows all highly radioactive components to be transported to a central hot cell facility without intermediate handling. The long high energy separated channels are housed in separate buildings or tunnels attached to the main experimental hall. To set the scale for the space required at the end of the secondary channels, schematic diagrams of existing experimental equipment have been included in the layout. Also shown are assembly areas, hot cells, active storage areas, counting rooms, 29 I / / L I / E a a E a tn a Figure 1: Layout of the primary and secondary beam lines 30 K 0 LOW ENERGY (pi,mu) K 1.5 -· ~~' HOT CELLS ---t-+~ ACTIVE STORAGE K 0.5 ~.AJ.~~t--- K 0.8 " .I..r __ -", t.4 S R AREA NEUTRINO FACILITY K 2.5 4~:::::"'--- K 20 /~ <:v ~ SERVICE BUILDING PROTON HALL LEGEND 51 51 B 51 BEAIot UNE cnI~EHTS r----"" r----, - COUNnNG ROOMS L... ___ .....J c=J c=J c=J POYtER SUPPUES IIE1ERS u.1! 1l111l1l_.J.............I---1.---J Figure 2: Proposed layout of the experimental hall 31 power supply mezzanines etc, all of which will be required for the effective operation of the facility. A polarized proton area has been envisaged between the two proton lines servicing the production targets. This area is provided with an independent proton beam from the Extender ring which is parallel to this ring. This geometry allows spin transparent beam optics to be employed from the extraction point to the experimental target. Therefore, the spin direction of the protons can be controlled in the accelerator. With the successful implementation of Siberian snakes and a laser pumped polarized ion source, it is expected to achieve 10 p.A of 70% polarized beam at 30 Ge V. Some consideration was given to the use of internal gas jet targets in conjunction with the polarized beam. Such a facility would require significant developments in polarized gas targets and in the understanding of beam losses in the Extender ring due to this target. It has therefore been left as a future possibility in the extraction hall. A neutrino facility, similar to the BNL facility, was designed to provide a wide-band neu-trino beam. This facility consists of a production target, a system of focusing horns, a decay tunnel and a long steel muon stop. Pulsed beams of protons are provided directly from the Driver ring. The production target and focusing horns have been located in the main experimental hall to allow access to the hot cell facilities. A separate experimental hall is required for the neutrino detector. The orientation of this facility is presently ar-bitrary. Long baseline neutrino oscillation experiments may require a definite orientation and may in fact determine the final position of this facility. The high energy separated beam lines, required for hadron spectroscopy experiments, are very long. In the case of the 20 Ge V / c channel the beamline components are housed in a tunnel. Buildings have been provided at the ends of these channels to house the detector systems. It is anticipated that the separation of these high energy particles will require superconducting rf cavities. Therefore, service buildings for refrigeration units and power supplies have been provided. Secondary Channels 1. General Properties The extraction of secondary channels from production targets is an essential ingredient in the design of the experimental areas. A study[l] was therefore undertaken early in the PDS to determine the relative merits of possible targeting and extraction schemes. In this study, six different secondary channel front-end configurations and three possible produc-t ion target arrangements were considered. It was found that a full range of secondary channels could be accommodated on a series of three in-line targets and that this arrange-32 ment would maximize the total kaon rate per incident proton. However, this did not allow the optimization of the individual channels and the operational coupling of the channels was extreme. A second arrangement which has four production targets arranged on two primary proton lines was chosen as preferable. This allows the optimization of each of the secondary channels and provides much greater operational flexibility. In the arrangement chosen, a high and low momentum channel are combined on each of two production targets with all channels viewing the targets at zero degrees. Two medium momentum channels are combined on a third target and a J(O channel taken from the fourth target. The layout for the high and low momentum channels is shown in Fig. 3. PROPOSED T2 TARGET STAnON ~ U u==t== -+--+----4---------------1> I \ \ \ \ \ IYACUUM BOX MODULES WELDED AT INTERCONNECnNG COLLAR \.. SlEEL Flll.ED. WATER COOL£D. SHIELDING BLOCKS i ~----------------4-0.00 METRES -------------------l Figure 3: Combination of a low and high energy channel with recombination of the proton beam and transport to a second target A 0.5 GeV Ic channel (KO.5) is combined with a 6 GeV Ic channel (K6) on the first produc-tion target and a 0_8 GeV Ic channel (KO.8) with a 20 GeV Ic channel (K20) on the second. It is necessary in this arrangement to reconstitute the proton beam and higher energy sec-ondaries using an achromatic system of bends after each of the secondary beam extraction sections. This allows each of the secondary channels to operate essentially independently. The possibility of avoiding the reconstitution of the proton beam by pitching it vertically before the production target was considered but rejected due to a number of serious prac-tical problems. This method increases the production angle of the high momentum beams, thus reducing their intensity, requires lambert son septa with small apertures which will 33 create secondary sources of contamination and has the proton beam passing far off the axis of the secondary channel quadrupoles which significantly increases the possible spills on the beampipe. Zero degree take-off is considered optimum for all secondary channels. It is essential for high momentum channels due to the fact that the production cross sections are strongly forward peaked. For lower momentum channels the channel acceptance can be maximized in a zero degree arrangement and the source size is minimized. The latter property could result in smaller and bet ter momentum resolution. It was found not possible to combine two medium momentum channels in a zero degree arrangement therefore the MAXIM system introduced by TschaHir[2] was used. In this system two bending magnets of opposite polarity are placed immediately after the production target. If the field parameters are chosen correctly the secondaries emerge from the second magnet in a direction which when projected back intersects the center of the target. This makes it possible to vary the momenta of the beams on either side of the proton beam independently. If the beams are of opposite polarity the production angle will be the same for both. If they are of the same polarity one of the beams will be viewing the target at a larger production angle which in many cases will lead to a reduction in intensity. In the above arrangements of secondary channels it is necessary to transport the proton beam which has passed through a production target to a second target. The first target will clearly limit the proton intensity transmitted to the second and target lengths will have to be chosen to optimally satisfy the experimental requirements. The targeting efficiency for such an arrangement was investigated in the study mentioned above. In this study it was found that secondary particle intensities from heavy metal targets do not increase for target lengths greater than 6 cm and that a 3 cm target gives 65% of the 6 cm. target rate. Multiple coulomb and nuclear scattering of the proton beam in the first target causes a halo on the beamspot at the second target. This halo could be important for the particle separation in the channels viewing this second target. Calculations indicate however that this halo is sufficiently thinly populated that its effect on contamination is comparable with other secondary sources and can therefore be dealt with in the same way. The main properties of the channels are summarized in Table 1 and the expected intensities for a 100 pA proton beam on a 6 cm long heavy metal target are given in Table 2. The calculation of these intensities is described below. 2. Channel Designs The channels described below have been optimized for high acceptance and high purity, with high purity being the primary consideration. Compared to existing channels the proposed beam lines are longer to incorporate the optics necessary to obtain the objective of an order of magnitude improvement in expected beam purity. 34 Table 1: Properties of Separated Beams at KAON Channel Momentum Solid Angle Momentum Length Type of Separation GeV/c msr Acceptance m ~p/p in % K20 20 -6 0.1 1 160 RF,3 cavities, 2.8 GHz K6 6 -2.5 0.08-0.30 3 110 RF, 3 cavities, 1.3 GHz K2.5 2.5 -1.25 0.5 -2.0 4 54 DC,2 stages K1.5 1.5 -0.75 2.0 4 30 DC,2 stages KO.80 0.80-0.55 6.0 5 18 DC,2 stages KO.55 0.55-0.40 8.0 6 14 DC, 1 stage, extra optics Table 2: Anticipated Beam Intensitiesa Channel P K K+ 7r 7r+ P GeV/c 106/s 106/s 109/s 109 /s 106/s K20 21 0.75 29 0.16 0.95 0.05 18 2.4 43 0.35 1.05 0.35 15 5.9 62 0.60 1.50 1.7 12 9.2 52 0.90 1.90 5.0 9 7.9 23 0.70 1.30 10.5 6 2.3 4.2 0.78 1.20 11.5 K6 6 15 34 1.9 3.6 23 3 2.5 4.5 3.2 5.0 43 K2.5 2.5 66 119 16 24 110 2.0 39 76 21 30 91 1.5 14 27 25 36 52 1.25 5.4 9.7 27 37 26 K1.5 1.5 193 366 49 69 81 1.2 52 93 36 49 25 1.0 18 31 27 36 8.3 0.8 3.7 6.3 18 23 1.9 KO.8 0.8 99 203 87 113 7.1 0.65 32 59 63 80 2.6 0.55 10 19 44 55 1.0 KO.55 0.55 41 80 80 101 1.5 0.50 21 44 67 82 0.93 0.45 9.2 21 50 61 0.53 0.40 3.8 9.4 33 44 0.30 .. aIntensltles are for a 100 J.lA 30 GeV beam on a 6 cm Pt target. 35 A study for a 3-6 Ge V I c separated beam[3] has shown that rf separators give an order of magnitude better separation than the present 20-30 m long dc separators. K6 and K20 (see Fig. 4) are rf separated beams consisting of three sections. The first section is an achromatic beam line containing two opposite bends. This section is used to define the phase space entering the separator section by a set of collimators and slits. The next section is parallel to the proton beam and contains three rf cavities which separate by giving transverse vertical kicks to the secondary particles dependent on their time of arrival at the cavities. Unwanted particles are removed by focusing them on a beamstop at the end of this section. The wanted particles travel around the stop and enter the last section where the beam is analyzed again to remove the remaining contaminating particles through momentum analysis. This section is achromatic and in addition to purifying the beam serves to prepare the beam properties required at the experimental target. The RF separators will have to be superconducting as they will have to be operated at high fields and in cw mode. The rf frequency is 1.4 GHz for K6 and 2.8 GHz for K20. The lower momentum 6 GaV / c KAON BEAMLINE RF1 RF2 RF3 J J J %~ ~ G{!a-------tHl-G---$- - ~ G-~ -~ 84 " ______ \JB 82 MASS 83 ~  SLIT 10m Figure 4: Layout of a high energy RF separated beam charged beams obtain a good purity using the technique of two stage dc separation. Fig. 5 shows the 0.8 GeV Ic channel (KO.8) which has been approved for construction at BNL to replace the existing LESB 1 channel. In this design the first separator causes unwanted particles produced directly in the production target to be vertically off axis at the first mass slit where they are removed. The remaining unwanted particles come from secondary processes such as the decay of neutral kaons and other particles near the production target, muons from the decay of pions after the first bend, and particles scattered on pole faces of magnets. The first mass slit defines a source for those particles and they are separated vertically at the second mass slit by 36 the second separator. Detailed calculations have carried out that which show that , indeed, a two stage separated beam has an order of magnitude better purity than a one stage sep-arated beam. Channel KO.5 is a shortened version of KO.8 to achieve the lower momentum PIWOUCTION TARGET , \ BtA ~LJtl~ MASS // SUI1 / ) SEPARAT OR MOMEIJ1UM _ V _~ SUT k 4.0m , '\ ') UASS SIII 7 ,(.\82 .r -···4750 C '- I ... .. Iffl"!. l OCUS Figure 5: Layout of the proposed 0.8 GeV Ic secondary beam with two stage dc separation range. This channel is 14.0 m long due to the extra optics required to include two stage separation. For lower momentum kaon beams this extra length seriously reduces the kaon flux due to decay in flight and eventually the beam purity will be dominated by this effect. In the region of 0.4 GeV Ic it is expected that a compromise will have to be made between the intrinsic quality of separation and the beam length. Below 0.4 GeV Ic the intensity decreases sharply due to both decay in flight and reduced production cross sections. A preliminary study was made of degrading a 500 Me V I c one stage separated beam down to 300 MeV I c. It appears possible to obtain a reasonable beam spot at the final target and a good purity. However, the momentum spread in the beam seems to be rather large, about 20%, which would make such a beam of limited use. Channels K1.5 and K2.5 (Fig. 6) as proposed for KAON are two stage separated beams. At present a channel is being constructed at BNL for 1.8 GeV Ic [4] with a similar layout. At KEK a 2.0 GeV Ic [5] channel will be installed in the near future which is a single stage separated beam where 37 - rv Q:- Q:- '-E '- E -- ;;f ~ ;;f ~ i{ !:i i{ !:i /:1 ~ /:1 ~ ~ -Q) DBBDO "~ ?OBBBO •• ij", 5.0 m IE )j 1.5 GeV / c BEAMLINE Figure 6: Layout of a medium energy secondary beam with two stage DC separation the source is defined very carefully at a vertical focus before the separator. The perfor-mance of the BNL and KEK beams will serve as guides for the construction of future channels in this momentum region. A number of channels will be used for experiments in hypernuclear physics and hadron spectroscopy where it is important to know the momentum of the incoming secondary particle to a precision of order 0.1 %. This precision is normally achieved by placing counters in the beam before and after the last magnet of the channel. However the channels at KAON are expected to have rates of 108/s to 109 /s and it is not clear that this approach will be possible. It may be necessary to add an extra analysing section to the channel for the purpose of obtaining good momentum resolution which for kaons can only be done at the expense of intensity. Clearly a compromise will have to be found for each individual experimental application. This problem is less severe for the high momentum channels such as K6 and K20 where additional analysis sections after the separation section can be provided with minimal loss of rate. It is clear that the matter of the resolution and the interplay of the beam line and ex-perimental spectrometer has to be investigated in more detail once proposals for specific experiments become available. The compromises involved can only be resolved by a close collaboration between experimentalists and beam line designers. 3. Production Cross Sections and Channel Fluxes The production cross sections for charged particles have been estimated using a combina-38 , tion of the Sanford-Wang [6] parameterization, a parameter set suggested by Yamamoto[7] and two experimental data sets obtained at energies close to 30 Ge V. These data sets are the 24 GeV cross sections for negative pions, kaons and anti-protons taken at CERN [8] and the measured fluxes from the LESBI and MESB channels at Brookhaven[9] for an incident energy of 28.5 GeV. Figure 7 shows the measured K- cross sections at 0° with the predictions of the Sanford-Wang and Yamamoto formulas as tabulated by Lobb.[lO] The predictions are clearly too low for momenta below 2 GeV Ic. Empirically a curve drawn through these data points has been used in the K- flux calculations. A possible explanation of the deviation of the z a I-a 0:: CL <..9 Z I-U <t 0:: W I-Z '-u '-> Q) <..9 '-... If) '-(f) W -.J U 0.01 ~ 0 .002 <t CL K ZERO DEGREE PRODUCTION OUR CURVE / " --- ........ - /// ' "-/. ~ / /-YAMAMOTO /. ~ y~ t ~ SANFORD - WA NG - CE RN A LES BI 0.4 0.6 0 .8 I 2 4 6 8 10 P(GeV/c) Figure 7: Measured K- production rates compared with several predictions measured cross sections from Sanford-Wang is that below about 2 Ge V I c the Sanford-Wang results come from kinematic reflection of higher momentum data. This ignores the kaons produced by secondary pions interacting again in the production target. A crude estimate of this effect gives a factor of 1.5 for the enhancement of low momentum kaon production, in rough agreement with the data. The Sanford-Wang formalism has been used to provide the ratios of K- :K+ or 7r- :7r+ . The ratio of p to K- cross sections is shown in Fig. 8. At high momenta the ratio is accu-rately predicted by Sanford-Wang while at 0.4 GeV Ic data from CERN and Brookhaven 39 are consistent but much higher than Sanford-Wang predicts. Again an empirical curve is assumed which is consistent with the data. The explanation for the deviation from Sanford-Wang is that the effect of the production target acting as a degrader for antipro-tons is neglected in the kinematic reflection. This effect gives a flux enhancement at low momenta where the energy loss in the target is comparable with the antiproton range (1 GeV Ic). The p cross sections calculated in this way are consistent with the model for p production proposed by Hojvat and Van Ginneken[ll], and with parameters modified as in the LAMPF II proposal. In general the cross sections determined by the various techniques are consistent within factors of 3 at low momentum and factors of 2 at higher momentum. --------_ .. _- - -----, 0. 1 • 0 - - CERN f- • LESSI <l: O.(l l n:: • • MESS 1 ::t:: '-IQ (l.(~() 1 / 0.0001 - ---1- - .1---' __ ---'. __ --'-_--'---1..--1 0.4 0.6 0.8 I 2 4 6 8 10 P(GeV/c) Figure 8: Ratio of p production to K- production The fluxes for the various beam lines have been calculated using the appropriate solid angle and momentum acceptance and correcting for the decay in flight between the production target and the end of the channel. The fluxes given in Table 2 assume a one interaction length target and operation at 100 p,A (6xlQ14 protons/s). 4. Neutral Kaon Beam A very important part of the experimental program involves the use of neutral kaon beams. As presently proposed this facility will be located at the second production target of one of 40 the slow extracted beam lines. The takeoff angle will be 6° to reduce neutron contamination and the total length of the channel will be approximately 20 m. The neutral beam is defined by a collimator (or two if the twin beam technique is used) which passes initially through a 10m long clearing magnet to remove charged particles followed by steel shielding to provide a total of 17 m of steel shielding equivalent. The neutron contamination may be further reduced with a 0.8 m long beryllium absorber which attenuates the neutron flux by about 20 times more than the KO flux. This leads to a neutron to Kf ratio of about 1:1. The twin beam technique would be used to reduce systematic effects and to provide nor-malization. Two identical collimators adjacent to one another produce two beams a few centimetres apart. A regenerator which can be switched from one beam to the other is used to provide a K~ component in one of the beams. For this technique to be successful the detector or spectrometer must be capable of associating events with one beam or the other with high reliability. The KO fluxes are shown in Fig. 9 as a function of energy. The fluxes have been calculated using an empirical formula where p = K momentum in GeV Ic () = production angle L = channel length in metres. x 107 u 10 -........ > QJ (9 8 -'-.. U QJ If) 6 -'-.. (f) W ...J K~ BEAM RATES SECONDARY L = 20m S1 =24f-Lsr 0 4 - WITH Be ABSORBER 1--0:: <! 2 -(L 0 .4 0.6 0.8 I 2 4 6 8 10 P (GeV/c) Figure 9: Neutral kaon beam rates from both secondary and tertiary production 41 The normalization, C, is taken from the Brookhaven beam[12] which has a solid angle of 10-4 , a takeoff angle of 6° and yields 3.3 x 1O-5K per proton on a 10.2 cm platinum target. The size of the beam spot is determined by the experimental requirements to be about 14 x 7 cm. This gives a solid angle for the proposed 20 m beam line of 24 x 10-6 ster. An option where 15 GeV pions are used to produce KO by the 7r- + Be -+ KO + X reaction has been studied. The KO flux obtained by using the 7r- beam from a 15 Ge V / c unseparated beam line is shown in Fig. 9. Although KO beams produced by this tertiary method would be very clean the flux appears to be uncompetitive as it is approximately a factor 300 lower than the secondary beam. 5. Muon Beams With 30 GeV protons it will be possible to produce muon beams, especially negative muons, with intensities greater than 60 times that available at the present meson factories. As the production of low momentum pions for decay channels, or surface muons is essentially isotropic, high acceptance channels could be installed at one or more of the production targets, with take-off angles of 90-135° to provide the high intensity muon beams. A beam line such as the upgraded M9 channel at TRIUMF with a superconducting solenoid would be ideal for the production of intense polarized negative muon beams. A high luminosity surface muon beam could be brought outside the shielding and then split between numerous users for Jl+SR studies. Both possibilities are indicated on the experimental layout. A further possibility is the production of pulsed muon beams using the fast extracted proton beam. Such a beam could be shared with the neutrino facility as the production in a backward direction would avoid interference with the pion horn. Unfortunately, for most of the pulsed muon work a pulse length of 100 ns (i.e. , a small fraction of the muon lifetime) is desired and the fast extracted proton beam has a pulse duration of 3.5 JlS which is not ideal for this work. Shorter pulse lengths could be provided at reduced av-erage beam intensity, however detailed study of these possibilities has not been carried out. 6. Neutrino Facility A neutrino facility taking full advantage of the intense fast extracted proton beam would make a major contribution to the physics program at KAON. In the initial stages, its de-sign would likely be based on existing facilities at other laboratories, but with the higher intensity of the primary proton beam at KAON, further development should lead to excit-ing new opportunities for neutrino physics research. A brief description of a neutrino beam line based on the wide band beam (WBB) at Brookhaven[13] is presented below; further details can be found in a recent design note.[14] An alternative facility is also discussed. 42 The most intense beams of interest are muon neutrinos produced by the decay-in-flight of pions and kaons via the reactions: ± ± (-) 7r -+ I-' v IJ ± (-) K± -+ I-' v IJ The pions and kaons are produced by bombarding a suitable target material with the 30 Ge V proton beam. These particles are then focused into a decay tunnel where the neutrinos are produced. A beamstop and long shield is then provided to absorb the primary beam and particles which have not decayed. The shield length is determined primarily by the requirement of stopping high energy muons. The target faces many ofthe problems common to all the targets at KAON. It must be able to withstand large mechanical and thermal stresses arising from the high instantaneous power from the pulsed beam, dissipate the high average power of the beam and have a high resistance to radiation damage. Some of the means for dealing with these problems are discussed in a design note by Terry Eaton[15]. However, since the neutrino facility target will be located inside the focusing device, space for containment and cooling is limited and special solutions will have to be found. Experience at BNL has shown that the largest neutrino yields are obtained using low density material, such as titanium. The BNL target is 50 cm long and 6 mm in diameter, and is contained by the magnetic horn used to focus the secondaries. Cooling is provided by the same water which cools the horn. Special care will have to be taken in designing a similar system for KAON because of the higher intensities involved and it is likely that the target and horn will be in vacuum. The pion production cross-section for 30 Gev / c protons peaks at a pion momentum of about 6 Gev/c and the production is small beyond an angle of about 6°. Therefore the pion focusing device specifications should include optimum focusing under 6 Gev / c, angular acceptance of approximately 6°, point-to-parallel focusing, wide momentum acceptance, minimal material in beam path, reliable operation, and polarity filtering. Generally an achromatic system consisting of a pair of magnetic horns is used. A toroidal magnetic field is produced around the secondary hadron beam axis which focuses hadrons of one charge over a large momentum band while defocusing the other charged state. The design of the pion horn system presented here is very similar to that used in the neutrino beam at Brookhaven and its performance was checked using the Monte Carlo simulation NUBEAM.[16] There are two pion horns as shown in Fig. 10 with the target located in the front of the first horn. The second horn about 7 m downstream produces a nearly parallel beam into the decay tunnel. The flux gain due to such a wide band horn is about a factor of 10. It should be possible to operate a pion horn of this type at 10 Hz but further development work is required to prove this. Like the target, the horn assemblies will be subject to increased thermal and radiation stresses due to the intense beam. Detailed study of these problems of remote handling and of alternative focusing 43 devices remains to be done. NEUTRINO FACILITY 1st PION HORN 2nd PION HORN I DECAY , I TUNNEL ~ 1.1 7 ViAI9 - ~.------.- -~ ?e LD 1.66 DETECTOR I Figure 10: Arrangement of the pion horns and decay channel for the proposed broad band neutrino facility The decay tunnel must be long enough to allow an optimum number of secondaries to decay and maximize the signal/background in the detector. It must be wide enough to accommodate as many as possible of the secondaries, especially those focused parallel to the beam axis. Therefore, its dimensions are dependent on the detailed design of the focusing system and of the detector. Similarly, the shield must be long enough to absorb all the remaining secondaries and their charged decay products. Calculations with NUBEAM indicate that the shield should be about 20 m long and the decay tunnel about 50 m long. The spectrum of neutrinos at the detector location obtained under these conditions, assuming 1013 protons on target and a detector diameter of 4 m, is shown in Fig. II. Besides the WBB discussed above, various refinements can be envisaged. For example, by utilizing a combination of plugs and collimators around the horns, mesons which are allowed to proceed to the decay tunnel can be momentum selected, thereby producing a narrow band beam (NBB) of neutrinos, whose momentum spread would be appreciably reduced from that of the WBB. However, this improvement is gained at a cost of about a factor of ten in flux; in addition, there are the added concerns of cooling the plugs and of servicing these extremely radioactive components. 44 --------_ .. ------------_. 0 Z 108 0::: I-:::> w 107 Z 106 ------105 0 I 2 3 4 5 6 NEUTRINO ENERGY (GeV) Figure 11: Calculated neutrino fluxes as a function of energy An alternative configuration for the facility might be used to optimize the production of a beam of electron neutrinos rather than muon neutrinos. This could be accomplished by replacing the horn with a dipole magnet to sweep charged secondaries away from the tunnel, leaving primarily a beam of K2. In this way, the ratio Ve : VIS can be increased to about 1:1 from the 1:1000 obtained with the horns. Again, this improvement is won at a substantial cost in flux. Another possibility would be to produce a tagged beam of neutrinos from K £3 decay. In this case, secondaries from the kaon decay are identified and their momentum measured in order to tag the type and kinematics of the neutrino produced. In summary, the higher intensity of the KAON Factory makes it possible to do experiments that cannot be done now, use a NBB where a WBB is currently used, reduce experimental running time or reduce detector size. The higher intensities also open the possibility of multiple detectors in the experimental area. 45 An entirely different type of facility could also be developed using the 3 GeV beam from the Booster rather than the full energy beam from the Driver . In this case, the beam would be allowed to impinge on a copper target where it would be stopped. Neutrinos would be produced primarily from 7r+ decay, producing qualitatively the neutrino spectrum shown in Fig. 12. W -.J () if) >-0::: <t: 0::: r-(l) 0::: <t: o 10 20 30 40 E (MeV) 50 60 Figure 12: Neutrino Spectrum from a Beam Stop Source Several new difficulties present theqlselves in such a facility; perhaps the worst is the pro-duction of a 3 Ge V beam from the Booster with appropriate time structure. The normal time structure of the beam from the Booster (pulses 720 ns long) is too long by about a factor of two. One possibility of modifying this structure would be to put two five-bucket holes in the beam in the Accumulator, and then after acceleration in the Booster, transport the beam to the Collector, where half the circulating beam would be extracted every 10 ms. Although little effort has been expended so far on the design of such a facility for the KAON Factory, it may be that the physics opportunities that would be opened warrant a detailed investigation. 46 TARGET AREAS 1. Introduction Perhaps the most crucial area to the successful operation of KAON is the design and implementation of the production targets, beamstops and all components in their vicinity. These areas must be capable of receiving and dissipating the full 3 MW of beam power delivered by the accelerators. This leads to difficult problems of power densities, component cooling, air activation and high levels of induced radioactivity. It is clear that detailed solutions to these problems can only be found when the secondary channels to be built have been completely defined. However, general approaches to these solutions can be investigated at this time. Considerable effort was made during the PDS to better define the shielding configuration around a production target with specific consideration given to a containment vessel to control air activation, component servicing and remote handling of components. Conceptual solutions have been found for most anticipated problems however much work remains to be done in prototyping before final design decisions can be made. 2. Targets The particle production targets to be used in the 30 Gev, 100 p,A slow extracted proton beam should be of high density material to minimize the secondary particle source length. In addition, the proton beamspot must be as small as possible (at least in one dimension) to facilitate secondary particle separation, a property crucial to the required high-purity kaon beams. The total power deposited in a 6-cm-Iong, 0.8-cm-diameter tungsten target by such a proton beam (x=y=1.5 mm)is calculated,using the FLUKA code[17], to be 160 kW, with a maximum deposited power density of 150 kW /cm. One method of dissipating this large power density is to spread the deposited power through a larger volume of target material by moving the target through the beam. This conventional technique also allows cooling over a much larger surface area and appears to be the best method of avoiding extreme power deposition. Two prototype targets exploiting this technique have been built and successfully operated in the laboratory. The first prototype[18] consists of an annulus of target material mounted coaxially on a water cooled spool. The flexible pipes attached to the spool serve both to supply the rotational drive and the cooling water. Fig. 13 shows the lower part of the target assembly. An upper section will provide the ferrofluid vacuum feedthroughs, rotating water couplings, rotation and drive motors. As these components are not radiation hard and manual servicing is required, a radiation shield is located between the target and upper section. The second prototype[19], shown in Fig. 14, is a novel design which uses the flow of cooling water to the target to power the target rotation. 47 ,-- ----7.500" (190.5mm) --------1 I TARGET MATERIAL EDGE - WELDED STAINLESS STEEL BELLOWS Figure 13: Mechanically driven bare rotating target '\ GRI\PIIALLOY \EARINGS - SIMULA TEO T ARGO ROTATION DETEClOR Figure 14: Water driven enclosed rotating target 48 The target material, in the form of a hollow cylinder, is mounted coaxially on a turbine which is free to rotate about a central water supply pipe on graphite bearings. Cooling water, supplied from a high-purity closed-loop system similar to that presently used to handle the highly activated water of the TRIUMF production targets, enters the centre of the turbine and drives the target rotation as it exits through slots in the turbine periphery. The symmetrical arrangement of these slots allows the rotational drive to be achieved without producing "end-thrust" on the bearings. The thick lucite containment jacket of the laboratory prototype would be replaced in an operational model by a stainless steel jacket. The proton beam would enter through a thin window in the jacket, pass through the target cylinder wall parallel to the rotation axis, and exit through a second window. Calculation of the temperatures and stresses that would arise during operation of both types of target have been carried out for various operating conditions. These calculations indicate that either target could be used in the slow extracted beam at full intensity. The problems associated with a production target suitable for use in the fast extracted beam are significantly different from those encountered with a continuous beam. Terry Eaton[15] has summarized these problems and suggested a solution using a combination of the rotating target concepts described above and the static graphite-encased-rod type of target in use at CERN, Fig. 15. The 4 times greater intensity per pulse required by KAON may be mitigated by increasing the beam spot size and the 100 times steady power level can be handled using target rotation. Unfortunately, such a target would be surrounded by a large amount of material and may not be suitable as a neutrino production target. With no significant focusing or defocusing of the primary beam between the production target and the dump, the maximum deposited power density in a solid copper beam dump would be 35 kW / cm. Unlike the situation at the production targets, a more flexible geometry is permissable, and several dump designs which reduce the deposited power density to manageable levels may be adopted. In one design a series of copper plates arranged perpendicular to the incident beam and cooled by water flowing between them is followed by a solid edge cooled copper block at a point where the energy density is sufficiently reduced. A more favoured technique, shown in Fig. 16 replaces the copper plates in the former design with an edge cooled section of graphite, thereby eliminating water from the path of the primary beam and the concommitant spallation and corrosion problems. Calculations using the FLUKA code to predict deposited power and the ANSYS program to evaluate generated temperature and stress fields in several dump geometries are continuing. 3. Activation and Remote Handling The interaction of the primary beam with the production target will cause a large fraction of the beam power to be deposited in the components and shielding close to the target and between the target and the beam dump. The deposited energy distributions for the 49 o 10CM U Figure 15: Production Target for the Fast Extracted Beam --- ----- ----- - -----.... ------------------------------------ .. ~ ," ~ , ( COPPER CAS~NG , \lATER JACKET r A ! ::i::;:!):::;<;:i:i:\:::!::»;:::::! l LA ~ GRAPHITE CORE ~ COPPER SLEE VE SECTION A-A .. _._ .. - _ .. _\ - . . - .. - .. - .. - .. ~ I \ u lJ -t-----t----- BEAM CENTRE LINE - - - 1--Jl ERNAL PIPING NET\loRK / INT FO R CODLING THE BEAM DUMP ; " r / 2 PIECE STEEL SHIELDING BLOCK n - - -100 0 oJ SECTION B- B PERIPHERAL COOLING PASSAGES COPPER CAS ING -·T·--/ r- B l - - - - -4-B r 100 200 300 400 500 CENTIMETRES Figure 16: Preliminary Beam Stop Design 50 " proposed target to beam stop geometry are shown in Fig. 17. The fraction of incident beam power deposited in the shielding and components between the target and dump is 45% (1.4 MW) with the remaining 55% (1.6 MW) being deposited in the dump. The deposited power density in any steel shielding or components positioned close to or a few metres downstream of a target will require the use of multiple cooling loops at radial distances up to 50 em from the proton beam. The complexity of the cooling loops could be considerably reduced by utilizing the high thermal conductivity of copper in these regions. The use of cooled copper shields where possible could also provide some reduction of power E (J) ~ o <t a:: 8 10 12 14 16 18 DEPTH (m) Figure 17: Contours of equal energy density in W /cm3 for 100 J-lA on an interaction length target surrounded by iron shielding dissipated in components further downstream. It is clear that in the detailed design of all components and shielding downstream of a production target significant attention will have to be given to the problems of beam heating. In addition to shielding, cooling will likely have to be provided for magnet pole tips and yokes which will add substantially to the complexity of the magnet design. Another consequence of beam losses in the target/beam dump areas is the production of high levels of residual radioactivity. Experience at TRIUMF, and at the other meson factories, has shown that the servicing and repair of highly radioactive components can be extremely difficult and time consuming. Therefore, the reliability and serviceability of any components in the vicinity of the production targets or beam dumps will be of prime importance in their design. Since 100% reliability cannot be assured, all such components 51 must be designed to be removed, replaced and/or repaired by remote handling techniques. This requirement makes it imperative that a remote handling philosophy be established at the outset of the project such that the design of all relevant components may conform to one standard system. The specific activity induced in components near targets and other beam spill points will be of the same order as in the present TRIUMF facility. The region of activation will however be much larger because of the much more extensive hadron cascade at the higher energies. This situation will largely void the previous strategy at TRIUMF of containing the highest activities at least from targets, inside monolithic shield blocks to make most of the primary beam line components approachable for installation and removal by hands-on or long-handle tools. The residual radiation fields from the more open geometry that may be required by the more extensive activation for bon factory beam lines could thus increase by more than the increased power factor and make such semi-remote manipulations very difficult, if not impossible. A study of remote handling approaches to be taken at KAON was undertaken by the Remote Manipulator Systems Division of Spar Aerospace Limited. The results of this study[20] confirmed that the vertical access canyon approach to component installation and shielding appears the most viable for the KAON target areas design. In this approach, components are installed in a narrow canyon and serviced by removal to a comprehensive hot cell facility via an overhead crane. Servicing in situ is not considered a viable option. In the conceptual design developed, a dexterous manipulator is used in conjunction with the crane to effect the removal and replacement of any components in a completely remote operation. The proposed hot cell facility consists of three cells. Two of these are intended to service highly active components such as targets, beam diagnostic devices and magnet components in close proximaty to the targets. A third, much larger cell, has been provided to allow servicing of large components with lower levels of residual activation. The size and shielding specifications of these cells has been based on the present experimental area design and estimations of expected residual activations. These specifications may have to be modified in response to changes in the area design. The hot cells are located in the main experimental hall within the coverage of the main building cranes. Since all production target areas are also within this coverage, the trans-portation of activated components to the cells will not involve transfer from one transport device to another. In the present concept, small components such as targets and beam di-agnostic devices will be transported to the hot cells in a shielded flask much as is presently done at TRIUMF. This is not possible with larger components as the combined weight of the component and flask will exceed the crane capacity. For these components, shield plugs will be attached where practical and a contamination containment vessel installed around the component before transport where necessary. Storage areas have been provided in the 52 vicinity of the hot cells for activated components which are inoperable or not in use. Figures 18, 19, and 20 show cross sections of typical shielded areas downstream of a production target. These illustrate the remote handling approach being taken in these areas. Individual components have a 2-metre thick steel shield through which all services are routed. CROSS SECTiON IHRU ?RIMAR"( L::<E ~EYC·.'A3LE CONCRE7E 5H!t: ... zm.c ~ iIi 1 I POWER , : ?O'A'ER ! ! SU?PLY I j SUPPlY: I I! '-j o 1 METERS L..L.Jr----------, Figure 18: Cross section through the shielding near a target location with a magnetic element installed All service connections are made at the top of this shield and will therefore not be required to be radiation hard. For larger components, part of this shield will have to be removable to keep the total component weight within the crane capacity. The services are connected and disconnected by a remote manipulator which is transported on a removable gantry placed over the working area. The manipulator and gantry are controlled from a remote station where closed circuit television and audio monitoring are provided. Control is expected to be primarily "man in loop", however automation may be possible for certain repetitive functions. The manipulator is intended to assist the overhead crane when heavy loads are to be handled and to operate specialized tools for such operations as disconnecting vacuum joints, checking alignment, leak detection, inspection etc. Services such as power and water will be routed through the concrete shield above the 53 ,NBIL.CAl '::C?O :0 g£"'O~E CON7RO~ .. <9 ) ~ ' !(3 ~, ..; . / ~ . ' ?b 'bo c~oss SEC . ON PR ;MAR Y lI!'J E . ~ :?r> " 0 .~ ~ 7HR U t.I[T[RS ~ Figure 19: Cross section through the shielding near a target location with a magnetic element removed SERVICE TOM:R TARGET LONGITUDINAL SECTION o METERS LL-.i SER VIC~ MANIFOlD AIR ENCLOSURE (COVER) RElAOVkBLE STEEL S~ I ELDI NG VACUUIJ CONNECTION Figure 20: Longitudinal cross section through the shielding near a target location 54 components as indicated in the sections. Control and monitoring devices such as valves and flow meters will be be located near the top of the shield so that they will be accessible with a minimum of shield removal. Fault diagnostics will have to be done outside the shield to localize defective components. 4. Shielding The design of shielding for these high beam loss areas is of major importance to the overall experimental area design. The required radiation shield is not only an expensive component of the experimental areas, and therefore must be considered carefully for cost optimization, it is also intimately connected to remote handling and component servicing considerations. As a result of these interactions and the cooling requirements in the target-beam dump regions, the detailed design of the shield will evolve along with the target, secondary channel, beam dump and remote handling designs described above. The cost estimates for the shielding are based on the quantities required to achieve the radiation fields in experimental and other areas described above. The unit prices for various types of shielding are based on present estimates and expectations, projected from past experience, for the material and fabrication costs. The total cost optimization for two component, iron and concrete, shields has been estimated approximately for a rough but realistic generic shield configuration. It indicates that at the unit prices expected the thickness of iron for minimum cost shields around high power meson production targets is in the 3-4 m range. The transverse shield requirement is dominated by hadrons produced in the target and the surrounding shield while the longitudinal requirement is dominated by high energy muons produced by pion decay. The total dose equivalent rate estimated at 10 m lateral distance from a production target removing ~ of a 100 pA, 30 Ge V proton beam through the 3.5 m iron and 2.5 m concrete shield shown in Fig. 18 is 0.2 p SvH-I. The estimate is based on the Moyer model[21] with the parameters cited above. [23] This very tight specification is of the same order as the cosmic ray background and is predicated on the probable requirement for very low background conditions for some of the secondary channel detector systems. For other directions, such as above the removable top shields the attenuation requirements can be reduced by an order of magnitude (or more) by the substitution of 0.77 m of concrete for iron or the removal of 0.46 m of iron or 1.15 m of concrete. The shield requirement in the forward direction is approximately double that in the lateral direction. However, beyond this depth there remains a substantial forward-peaked beam of muons with ranges up to 15 kg cm-2 • The problem of muon penetration of thick shields has no analog at lower energy facilities like TRIUMF where the muon range is short « 1 m of concrete) but is well known at existing high energy facilities. It arises because muons have no appreciable nuclear reaction probability and are too heavy to radiate significantly. Sullivan's[22,24] empirical description of the experimental measurement results for the muon intensity can be recast 55 in terms of dose-equivalent to give E .~ -..JI....d' D.E. = 3.4 x 10-9 ~ e Ep "SV perproton (1) for muons surviving to a depth d (in metres) in a monolithic iron shield from the decay of pions produced by the non-elastic nuclear collisions of protons of energy Ep (in Ge V) in the iron. The parameter a is an effective relaxation constant that has values of 22 Ge V m- I for iron and 7.8 GeV m- I for concrete independent of proton energy, at least for Ep up to 30 GeV. The ~ parameter is the flight path distance for the decay of the pions. For a continuous beam stop/shield, d' = d and ~ is the mean free path before pion-nuclear collisions, 0.3 m in iron, 0.8 m in concrete. For targets/beam stops with intermediate voids the point decay length must be increased directly and the d-2 geometry factor and the exponential relaxation distance d' adjusted accordingly. Equation 1 is normalized to 1 proton incident and estimates the maximum dose-equivalent rate in the coincident directions of the original proton and decaying pions beams. For off-axis directions the measured muon intensities decrease with an approximately Gaussian dependence with a half-maximum diameter, w, dependence of For 100 pA of 30 GeV protons on a monolithic iron beam stop/shield the estimated dose equivalent rate at 20 m (15 kg cm-2 ) depth near the end of the maximum muon range is 70 pSv h- I , with half-maximum intensity diameter of 0.8 m. For a 3 m pion decay void following an initial 0.3 m target the muon intensity would increase to a factor approaching 3/0.3=10. These estimates indicate the need to range out all muons downstream of high intensity spill pion with approximately 150 tonne m-2 shield thickness. The total saturated source strength of the, mostly short-lived, radioactive species produced in the air in the vicinity of the TRIUMF production targets and beam dump is approxi-mately 4 x 109 Bq at 50 kW beam power. Because a much larger fraction of the hadron cascade is developed down-beam of the KAON production targets the total source strength in an air atmosphere around these components is expected to be even greater than a simple extrapolation of a the beam power would indicate. Table 3 shows anticipated saturated source strengths of the major radioactivation isotopes for a dry-nitrogen atmosphere sur-rounding the down beam components. The yields for an air atmosphere would not be significantly different. 150 at yields comparable to those for 140 and 18F at less than 1 % of the major contributors would be the only additions. The major difference between an air and an all nitrogen atmosphere would be in the radiolytically induced molecular combinations produced. Dry air under hadronic cascade bombardment will contain ozone and various oxides of nitrogen. Any moisture present would result in a dilute nitric acid atmosphere which could be very corrosive. 56 To avoid intolerable contributions to personnel radiation doses, both on and off-site, but more particularly intolerable contribution to background in large sensitive detectors in the secondary experimental areas, it will be necessary to achieve good containment of the atmosphere down-beam of the primary KAON production targets. The atmosphere must also be very dry, especially for air, to avoid corrosion. The over-riding problem with an air or nitrogen atmosphere is likely, however, to be associated with the long lived (53 day half-life) 7Be radioisotope. Even if the air or nitrogen is recirculated through high efficiency filters a significant fraction (say 1 to 10%) is likely to contaminate all components inside the atmosphere enclosure at the 103-104 Bq cm-2 level. Although this level would not by itself represent a serious local problem, the combination with the residual radiation fields expected from imbedded radioactivity (1-10 mGy h- I ) and its general extent will produce a non-trivial and potentially expensive constraint on maintenance operations. The above contamination problem would be largely avoided by using a helium atmosphere around the KAON production targets and downstream components. Based on our current experience the removable surface contamination and filter radioactivity inventory, consist-ing mostly of recoil radioisotopes from bombarded metal components, would be at only the 1 % level of that quoted in Table 3 for 7Be. The use of a helium atmosphere however presents some additional difficulty of achieving an adequate environmental seal and would necessitate using a different gas for vacuum seal testing. Table 3: Radioisotope Production from Hadronic Cascade on Nitrogen Yield per Saturated Dose Rate Radioisotope Collision Source Strength @lm Bg mGy h- I 140 .04 6.5 x 1011 320 13N .04 6.5 x 1011 100 lle .08 1.3 x 1012 200 7Be .06 9.0 x 1011 7 3H .11 1.8 x 1012 (Note: Normalized to 3 MW intercepted beam power 50% iron, 50% nitrogen (by volume) assembly) . 57 PRIMARY PROTON LINES The experimental areas as designed require four proton beams from the accelerators, three from the Extender ring and one from the Driver. It is possible that all these beams could be required to be operational at the same time. Also, the slow extracted beams will likely be required to be split in continuously variable ratios. To accomplish this, two beam splitting sections have been provided in the slow extracted beam. These consist of electrostatic and magnetic septa similar to those used for the slow extraction process and are described below. The splitting scheme designed by L. Criegee[25] gives four possible beams from the Extender ring. One of these slow extracted lines is not used in the present facilities and is therefore available for future expansion . . The slow extraction system has been described in some detail in Section 2.2.3 of the accelerator design report . It is accomplished with a 3-element configuration consisting of an electrostatic pre-septum and septum, each of which deflect in the horizontal plane, and a magnetic septum which bends vertically. A reverse bend then brings the beam back into a horizontal plane 0.75 m above the Extender ring. A similar system is proposed for the continuous splitting of this extracted beam. For this purpose a special high-,8 section has been designed with quadrupoles spaced alternately 10 m and 3 m apart. There are six periodic sections, each period having a length of 16.5 m. A preseptum initiates a split between the lines feeding the two main target areas in the experimental hall. Splitting is accomplished with a preseptum, 0.5 m long with a symmetric field of ±50 kV jcm, an electrostatic septum, 5 m long and also symmetric with ±50 kV jcm, and a magnetic septum identical to that of the Extender ring. The magnetic septum bends one beam down and a subsequent reverse bend brings it into the horizontal plane at the same elevation as the Extender. By steering the extracted beam across the preseptum the fraction of beam sent to a given area may be varied continuously. Each of the above beams can again be split in a similar manner giving in principle four separate beams. In the present design only one such split has been provided which allows beam to be delivered to the polarized proton area. This beam is bent horizontally such that it enters the experimental hall parallel to but offset from the Extender ring. This ensures that the beam transport is spin transparent so that the spin direction can be determined at the point of extraction. All the extracted beams are bent vertically such that they enter the experimental hall at the elevation of the Extender ring. TRANSPORT and REVMOC calculations verify the design parameters of x = ±2.6 mm and y = ±1.3 mm at the target locations. Figure 21 shows a top view of the beam splitting to the various areas; a side view is shown in Fig. 22. A preliminary design has been done for the fast extracted beam. This beamline will transport the beam extracted from the Driver ring to the neut rino target area. Its first 58 20 10 ---... E '-../ X ~PS1 .MS1 .PS2 ~MS2 0 .j..PS3 J..MS3 tES1 [521 -10 -50 o 50 100 150 200 250 300 Z (m) Figure 21: Top view of beam switchyard 1.0 0.5 B P A >-0.0 -0.5 -50 o 50 100 150 200 250 300 Z (m) Figure 22: Side view of beam switchyard 59 elements, a kicker magnet, 3 septa and a dipole, are identical to those of the D to E transfer line (see section 2.2.2 of the Accelerator Design Report). These horizontally-bending elements are followed by a series of quadrupoles and dipoles configured to produce a reverse horizontal-bend system which is doubly achromatic and which, at its exit, gives a separation of 2.5 m between the fast extracted beam and the Driver staight. In addition, the design is such that the beamline matches into a FODO array identical to that in the long straight of the Extender. This is done because of the long distance to the experimental area. Because the beam line is in the same plane as the Driver and Extender, it is necessary to provide some verticl displacement to avoid interference between components of the fast extraction line and Driver and Extender rings. A vertical separation of 1 m between their beam planes is accomplished with a double-reverse vertical bend scheme. This vertical separation is maintained into the experimental hall due to possible interference with com-ponents of the of the slow extracted beams, A second reverse vertical bend then brings the beamline down 1 m to the same elevation as the other beam lines. A top view of the beam line is shown in figure 23; the straight section at x = 0 m is the long straight section of the Driver. Figure 24 shows a side view; to avoid confusion, the Driver straight is omitted here. 20. 15. ,-...... 10. E X 5. o. -5. a 50 100 150 200 250 300 350 400 450 Z (m) Figure 23: Top view of the fast extraction system 60 1.5 to 0.5 >-0.0 -0.5 a 50 100 150 200 250 300 350 400 450 Z (m) Figure 24: Side view of the fast extraction system In the section which lies 1 m above the Driver and Extender is a FODO array, with the same quadrupole spacing as the Extender, and a horizontal bend of -7 degrees. The latter directs the beam to the neutrino area. Design of the vertical displacement section, including the horizontal bend, is such that at its exit the beam is dispersionless in each of the horizontal and vertical planes. In addition, properties of the beam are matched into a FODO array identical to that of the Extender. This allows for further transport to the neu trino area. It must be anticipated in the slow extraction and beam splitting processes that beam losses will occur. Therefore, a long extraction building has been provided which covers the entire length of the slow extraction and beam splitting elements. This building with its overhead cranes allows vertical access to all components inside via removable shielding. In this situation some beam loss on components can be tolerated as components can be handled in much the same manner as envisaged for the target areas in the experimental hall. If necessary, the same remote handling techniques could be employed. Calculations [25] indicate that beam losses should be low in the beam splitting process. However, in the initial operation it is intended to share the proton beam in a much simpler pulse by pulse . mode until experience with the slow extraction system has shown that the continuous splitting of the proton beam can be done with beam losses sufficiently low that components in the beam lines will not be radiation damaged. Once the beams have been split, losses are expected to be very low and therefore the remaining beam transport components have been placed in a tunnel which connects the extraction building with the experimental hall. 61 References [1] J. L. Beveridge and J. Doornbos, Layout of Secondary Beams at KAON, TRI-DN-89-KI9. [2] C. TschaHir, Multiple Achromatic Extraction Systems, NIM 249 p.l71 (1986). [3] Proceedings of the International Workshop on Hadron Facility Technology, Los Alamos, February 1987, Los Alamos report LA-I1130-c, UC-34 and UC-28, page 531: RF separation in a 9-6 Ge Vic kaon beam. [4] Philip H. Pile, Beams for Kaon Research Nuclear Physics A450 5176-5326, 1986. [5] T. Nagae (INS), M. Ieiri (KEK) High Resolution Spectroscopy above 1 Ge Vic, Pro-ceedings of TRIUMF /KEK Workshop on Hypernuclear Physics at KAON, p.259-275, 1989. [6] J. R. Sandford and C. L. Wang, Empirical Formulas for Particle Production in p- Be Collisions between 10 and 95 Ge Vic BNL 11299 (1967) [7] W. Yamamoto, Study on Low Energy Intense Kaon Beam K£ Thesis, KEK. [8] J. F. Amann, et al., Measurement of Production Cross Sections for Negative Pions, Kaons and Protons at 10, 18 and £4 GeVLos Alamos Report, LA-9486-MS (1982). [9] G. M. Bunce, A GS Beams, May 1968, BNL 50874 (1978). [10] D. E. Lobb, Sanford- Wang Results for 1£, 18 and £4 GeV Protons. [11] C. Hojvat and A. Van Ginneken, Nucl. Inst. Methods 206, 67 (1983). [12] W . . M. Morse et al. Search for the Violation of Time Reversal Invariance in K~.3 decays Phys. Rev. D21 1750 (1980). [13] D. H. White, The AGS Broad Band Neutrino Beam, BNL 36278 (1985). [14] R. H. Helmer, A Neutrino Facility at KAON, TRI- DN-90-K117. [15] T. Eaton, A Target Design Study for the Fast Extracted 10 Hz Beam, TRI-DN-89-K41. [16] C. Wisser, NUBEAM Neutrino Beam Simulator, Hydra Applications Library, CERN 1979, modified by R. Carlini, Los Alamos National Laboratory. [17] G. R. Stevenson, J. Ranft et al FLUKA '86 Users' Guide, CERN Report TIS-RP/168. [18] T. A. Hodges and R. R. Langstaff, Prototype "Bare" Rotating Target, TRI-DN-90-K11l. [19] T .A. Hodges, R. R. Langstaff and M.S. Lenckowski, Laboratory Prototype of Rotating Immersed Target, TRI-DN-90-KI10. 62 [20] Final Report of the KAON Factory Remote Handling Study, Spar Aerospace Limited (1989). [21] R. H. Thomas and G. R. Stevenson, Radiological Safety A"pect" of the Operation of Proton Accelerator", Technical Report Series No. 283, International Atomic Energy Agency, Vienna (1988). [22] A. H. Sullivan, A Method of Estimating Muon Production and Penetration Through a Shield Nuclear Instruments and Methods in Physics Research A239 (1985) 197- 201 [23] TRIUMF Accelerator Design Report Chapter 7, p.2 (1990). [24] Proceedings of the Worbhop on the Production and Transport of Secondary Beams at a KA ON Factory. Ed. D. R. Gill, Vancouver, June 2-4, 1986, p97. [25] L. Criegee, A Study of the Slow Extraction at the KA ON Factory, TRI-DN-89-K78 63 


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