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Proceedings of the charge-symmetry breaking workshop, Vancouver, March 26, 1981 Davison, N. E.; Svenne, J. P.; van Oers, W. T. H. Jul 31, 1981

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TRI UMFPROCEEDINGSOF THECHARGE-SYMMETRY BREAKING WORKSHOPVANCOUVER MARCH 26, 1981Editors: N.E. Davison, J.P. Svenne and W.T.H. van OersDepartment of Physics, University of ManitobaMESON FACILITY OF:UNIVERSITY OF ALBERTA SIMON FRASER UNIVERSITY UNIVERSITY OF VICTORIA UNIVERSITY OF BRITISH COLUMBI TRI-81-3TRI-81-3PROCEEDINGSOF THECHARGE-SYMMETRY BREAKING WORKSHOPVANCOUVER MARCH 26, 1981Editors: N.E. Davison, J.P. Svenne and W.T.H. van OersDepartment of Physics, University of ManitobaPostal address:TRIUMF4004 Wesbrook Mall Vancouver, B.C.Canada V6T2A3 July 1981PrefaceTABLE OF CONTENTSPagevSession IC.-Y. CheungCharge-Symmetry Breaking in the Neutron-Proton System ........... 1A. GerstenCharge-Symmetry Breaking in the n-p Interaction .................  3L.D. KnutsonStatus of the Wisconsin-Indiana Charge-Symmetry Experiment .....  6L.G. GreeniausTest of Charge Symmetry in n-p Scattering ....................... 8C . L . Hoi 1 asA Test of Charge Symmetry in the np diT° Reaction at 795 MeV ... 12General Discussion ...................................................  15Session II G.A. MillerComparisons of ir±d Interactions and Charge-Symmetry Breaking .... 16 T.G. MastersonCharge Symmetry and the ir±d Interaction ..........................  18B.M. PreedomProposed Measurement of the Reaction d+d -* irC)+1+He by the Neuchatel-Grenoble-Saclay-Orsay-South Carolina Collaboration .... 20S.A. CoonCharge Asymmetry in the A=2 and A=3 Nuclear Systems ..............  22Evening Discussion Session .............................................  27Recommendations .........................................................  32List of Participants .................................................... 33PREFACEA one-day workshop was held on March 26, 1981 at the Meson Physics Facility TRIUMF in Vancouver on the topic of ‘Charge- Symmetry Breaking1.The workshop's purpose was to bring together theorists and experimentalists involved in studying various aspects of charge- symmetry breaking. In particular, its main goals were to review the existing theoretical predictions, to examine the importance of the various contributing effects to charge-symmetry breaking and to define the sensitivity required of experimental tests of charge symmetry in order to be meaningful. The results of the workshop are formulated as recommendations for future theoretical and experimental work in this area. The workshop has also defined a framework for the parameters being determined in a new series of experiments testing charge symmetry.The workshop was attended by 36 delegates, a number which allowed active participation by all and lively and exciting dis­cussions. The contents of the Proceedings of the workshop con­sist of summaries of the invited presentations (provided by the respective authors), the discussions following the presentations and finally, in abbreviated form, the discussions of the evening session and a formulation of recommendations.Thanks are due to the chairmen of Sessions I and II, E.M. Henley and W.J. McDonald, respectively, and during the evening session to B.F. Gibson for guiding the discussions. Thanks are also due to TRIUMF and to the TRIUMF Users organization for their financial support without which it would not have been possible to organize the workshop. Assistance was also rendered by the TRIUMF staff. Finally, Ada Strathdee has been responsible for the preparation of these Proceedings in their final presentable form.W.T.H. van OersvSESSION ICHARGE-SYMMETRY BREAKING IN THE NEUTRON-PROTON SYSTEMC.-Y. CheungDepartment of Physics, Carnegie-Mel 1 on University, Pittsburgh, Pennsylvania 15213Theoretically there are two classes of CSB (charge-symmetry breaking) forces, namely those of class III and class IV given by VIII(i,j) =A(r3 (i) + T 3 ( j ) )  and VIV(i,j) = B^x3(i) - ^ 3(j)) + c(x(i) * x(j)j3, res­pectively. 1 Only Vjv(i,j) affects the n-p system. Two consequences of CSB in the n-p system have been examined. 2 The following is a summary of resu1 ts obta i ned . 3PpU-The(a) n-p Elastic ScatteringCharge-symmetry implies that Pn(0c.m.) = of CSB interactions would spoil the symmetry.A (0) = Pn(®c.m.) “ Pp^-^c.m.) has been calculated tions on the basis of one-boson-exchange mechanisms. Figure 1 summarizes the results obtained. We note that the effect due to p-to mixing (Ap-^) is negligible, and the direct electromagnetic contribution (Ay ) dom0c.m.)- The existence asymmetry parameter for three CSB interac-inates A(0) at 0c .m. < 40c In practice, anull experiment can be done more accurately. Charge symmetry is broken if precise measure­ments show that Pp and Pn cross zero at different angles in the c.m. frame. This difference is roughly 0.5° from Fig. 1 and is dominated by the effect of n-p mass dif­ference (Afi) at Ejai-, = 300 MeV.0cm _(deg)Fig.Elab'c.m.1. Polarization difference at = ZOO MeV.0, m. toeg)'c. .Fig. 2. Angular asymmetry in  np ■* d-n0 at Flab = MeV.(b) np -> dir0One consequence of isospin conser­vation in this reaction is the symmetry of the differential cross section about 6c.m. = 90° > that is, do(ec .m J/dn = do(Tr-eC-rTK)/dft. The presence of cl ass IV interactions would cause the angular distribution to be slightly asymmetric about 90°. The symmetry-breaking effect A(e) = da(ec-m)/dft - da(TT-0c .m ,)/dfi has been calculated for four CSB interac­tions (Fig. 2). Within the model described in Ref. 2, the n - ^0 mixing mechanism gives the largest front-back asymmetry of about -0.7% (Ap-^) . The2effect of n-p mass difference (A<$) is about one-fifth of A^-^, and con­tributions due to one-photon exchange (Ay) and p-u mixing (Ap-^) are negli gi ble.Apart from the symmetry in the angular distribution, isospin conser­vation also implies that the polarization of deuterons, Pd(0c.m.)» >s symmetric about 0c .m . = 90°. A measurement of the asymmetry in P<j constitutes another test of charge symmetry in the np -*■ dir0 reaction. The sensitivity of this test to various CSB mechanisms might be different from the one described above.References1. E.M. Henley and G.A. Miller, in Mesons in nuclei, eds. M. Rho andD.H. Wilkinson (North-Hol land, Amsterdam, 1979), p. **05.2. C.-Y. Cheung, E.M. Henley and G.A. Miller, Nucl. Phys. A3^8, 365 (1980). 3- For the results of a different calculation, see A. Gersten, theseproceedings, p. 3 .DISCUSSIONFRIAR, BONNER and GERSTEN raised questions on various points of detail in the calculations.COON: The value of g^ used is approximately 20 times higher than thelatest experimental value.BONNER: 1) In np -*■ dir0 , the intermediate A0 and A+ have different massesand widths; their effects should be taken into account. 2) Two-pion- exchange effects should be calculated.CHEUNG: There are too many diagrams; it does not seem worth while tocalculate them all at this stage.DAVISON: How accurate and reliable are calculations of direct electromag­netic effects?HENLEY: One experiment will not provide the answers on CSB— one needsconsistency among a series of experiments and the same model.FRIAR agreed.KNUTSON: Many important graphs have not been calculated.HENLEY: No one is going to calculate them until there are experiments ofsufficient accuracy.3CHARGE-SYMMETRY BREAKING IN THE n-p INTERACTIONA. GerstenTRIUMF and Department of Physics, University of British Columbia,Vancouver, B.C., Canada V6T 2A6andDepartment of Physics, Ben-Gurion University of the Negev,Beer-Sheva, IsraelThe possibility of mixing isospin states in the n-p interaction was indicated recently in several works, where some estimates of the effects were given . 1 - 5  It seems that in order to incorporate well the efforts a simplified formalism or approach is needed. The main purpose of this work is the development of such a formalism and the indication of the main sources of isospin mixing.In Ref. h it was proposed to use the following parametrization ofthe transition between the singlet (L=J, S=0) and uncoupled tripletstates (L=J, S=l) which are states of different isospin<J1|T(J)|J0> = ~y sin 2yj exp(iSj + i6jj) , (l)where 6 j  and PR R are the bar singlet and uncoupled triplet phase shifts, respectively; y^ 's the new bar mixing angle parameter of the singlet- triplet transition. The scattering matrix was described with the aid of six amplitudes, and it included the isospin-violating amplitude f(0) in the following form f(0)[(an-crp) • n]. It was found that the amplitudef (0) is simply related to the matrix elements of Eq. (1) in the followingwayCOf(e) = i  E  (2J+,) Sin 2^J exP[J^ J  + ^JJ) ]d 10 (0) . (2)J= 1 Jwhere k is the c.m. momentum and d 10 are the Wigner functions.The total phase shift 6 is given by6 = SN + 6nc + 6EM » (3)where 6^ is the nuclear phase shift calculated without electromagnetic effects, Sem 's the Coulomb phase shift and is the contribution of the interference of these two processes. Above approximately 20 MeV the following approximations seem to work quite well:6 + 6EM + 5NC »Bwhere is the electromagnetic phase shift in the first Born approxi­mation. In Ref. A we found a very simple expression for the electromag­netic phase shifts in the first Born approximationYjM = n vn k2/[M2 /j(J+l)] , (5)where n is the Coulomb parameter, vn is the absolute value of the anoma-'lous magnetic moment of the neutron and M is the nucleon mass.We make the replacement sin 2yj o* 2yj, as yj is very small and re­write Eq. (3) in the following way:f(e) > {  E  (2J+ l ) [ ( ^ X i V j C) e x p ^ + j J j )  - 7 5 M]<ilo(6)j  1invnk2sin0M (1 -cose) ’ (l }where the last term on the r.h.s. of Eq. (6) is the resummed electromag­netic contribution. The phases 6j and 6jj are almost unaffected by the electromagnetic interaction; therefore, their values can be taken direct­ly from phase-shift analyses.At present it is rather impossible to make an accurate evaluation of the Yj. Expressions in the first Born approximation are given in Ref. 7 for some of the possible processes. This is done in order to have esti­mates on the order of magnitude of the possible effects. The expressions were derived using Eq. (2) and the techniques of Ref. 6 . We list here the effects only, the detailed expressions and results are given in Ref. 7-1) Neutron proton mass difference inthecharged one-pion exchange diagram2) o),p° mi xi ng3) Neutron proton mass difference in the charged one p meson exchange diagram.In Fig. 1 of Ref. 7 we display the energy dependence (up to 750 MeV lab energy) of the resulting mixing angles yj for the above three pro­cesses as well as the electromagnetic Yj^. For J > 3 the electromagneticand OPE contributions dominate. In the N-N interaction the mixing angles Fj of the coupled triplet states for J > 3 are dominated by the OPE. We can expect also such a dominance for yj for J > 3- Hence we can make a further simplification and approximate Yj by the first Born approximation of the OPE contribution. Thus we are left with three undetermined mixingangles Y2 » Y^ f which should be responsible for the main features ofthe isospin-violating amplitude f (0) of Eq. (6).In Fig. 2 of Ref. 7 is displayed the polarization difference of the neutrons and protons resulting from the charge symmetry nonconservation for lab energies 200, 325, 500 and 750 MeV. In these figures only the electromagnetic contribution is expected to be quantitatively well described, while the other contributions should be treated as indicating the order of magnitude of the effect. For this reason we do not give a total polarization difference.In conclusion it seems that a simplified treatment of the isospin- violating amplitude f (0) is quite plausible in terms of Eqs. (6) and (5). For J > 3 the OPE contribution can be used as a good first approximation.The process thus should be described with the aid of three parameters1, 1 1,1______k I 1Yy» >2 , Yg• In this work we give an estimate of their order of magnitudeand correspondingly the expected magnitude of the difference in thepolarization of the neutrons and protons.1. E.M. Henley and G.A. Miller, in Mesons in nuclei, eds. M. Rho andD. Wilkinson (North-Hol1 and, Amsterdam, 1979), p.405;C.Y. Cheung, E.M. Henley and G.A. Miller, Nucl. Phys. A305, 342 (1978).2. S.A. Coon, M.D. Scadron and P.C. McNamee, Nucl. Phys. A287, 381(1977); Nucl. Phys. A249, 483 (1975).3. C. Lechanoine, F. Lehar, F. Perrot and P. Winternitz, Nuovo Cimento 56A, 201 (1980).4. P. La France and P. Winternitz, J. Physique Vl_* 1391 (1980).5. A. Gersten, Phys. Rev. C _I8^ 2252 (1978).6 . A. Gersten, P.A. Verhoeven and J.J.deSwart, Nuovo Cimento 26A, 375, (1975).7. A Gersten, TRIUMF preprint TRI-PP-81-11.4DISCUSSIONG. MILLER: Is the Born approximation adequate for <$EM?GERSTEN: Yes, if the direct Coulomb contribution is resummed (Eq. 6).CHEUNG: At large angles, a partial-wave expansion is all right.GERSTEN: Not necessarily. In pure Coulomb scattering, the partial-waveexpansion is divergent everywhere (contrary to a published and much quoted statement by Breit that it is slowly convergent for 0 ^ 0 ) .HENLEY: Have ir-product ion effects been included above 400 MeV?GERSTEN: Partly, in that the imaginary parts of the strong-interactionphases have been taken into account.COON: Is it not better to do amplitude analysis?GERSTEN: No, the strong phase-shift analysis is totally insensitive toCSB.DAVISON: Can we get a detailed comparison between the Cheung and Gerstenca 1culat i ons?[provided later, in general discussion session, p. 1 5]56STATUS OF THE WI SCONS IN-INDI ANA CHARGE-SYMMETRY EXPERIMENTL.D. Knutson, S.E. Vigdor, J.G. Sowinski, W.W. Jacobs, A.D. Bacher,D. DuPlantis, C. Glover, B.P. Hichwa, P.L. Jolivette, H.-O. Meyer,G.B. Orr, P.A. Quin, P. Schwandt, E.J. Stephenson and D. WarkWe are planning to carry out a sensitive experimental test for the presence of charge-symmetry (CS) breaking forces in the n-p interaction.It is well known that if CS invariance holds the analyzing power for the scattering of polarized neutrons from unpolarized protons (An) and the analyzing power for the scattering of unpolarized neutrons from polarized protons (Ap) must be equal. The planned experiment will be carried out at the Indiana University Cyclotron Facility at a neutron energy of 200 MeV.The order of magnitude of the expected CS violation at En = 200 MeV is illustrated in Fig. 1. Here A = ^(An+Ap) and AA = An-Ap. This calcu­lation includes the isospin violating P- and D-wave mixing parameters (calculated in Born approximation1) which arise from the effect of the n-p mass difference on the one- pi on-exchange potential. For ®c.m. = 90° we obtain AA ta -0.005. Calculations of p-ui mixing predict CS violations of about the same magnitude. 2In the experiment we will measure left-right asymmetries, to an accuracy of approximately ±5X 10_1+, in the scattering of polarized neutrons from polar­ized protons for c.m. scatter­ing angles between 7 5° and 120°. Various polarization states of the beam and target will be used. The greatest sensitivity to CS breaking is obtained for cases in which the beam and target polarizations are equal and opposite. CS violations of |AA(90o)| > 0.001 will be detectable, without the need for precise measurements of the beam and target polarizations. This will be done by forming ratios of analyzing powers for different scattering angles,i.e., F(0x,02) = [An (01 )Ap(e2 )/An (02)Ap(e1)]. Deviations of this quantity from unity indicate the presence of CS violation. This procedure could fail to detect the CS violation if A and AA happened to have identical shapes. However, at 200 MeV A crosses zero at 90° while the contribution to AA from 3P^-1Pj mixing is maximum at this angle. Thus we will be able to detect P-wave mixing if it occurs. The experiment will be relatively insensitive to CS breaking in the even partial waves since the contribu­tions to AA cross through zero at 90° for these cases.n -p  SCATTERING, Elob= 2 0 0  MeVFig. 1. Phase-shift calculations o f  the average A(9) and o f  the difference AA(6)  o f  neutron and proton analyzing powers fo r  n-p scattering at Elab ~ 200 MeV. P-wave and D-wave isospin-mixing parameters are taken from Ref. 1.7The polarized neutron beam for the experiment will be produced by charge exchange of a 200 MeV polarized proton beam on a liquid deuterium target. A beam intensity of about 5 x 101* neutrons/cm2-sec and a polari­zation Pn 2*0.65 is expected at the target position. The polarized target will be a "spin-refrigerator" , 3 which offers the advantages of modest mag­netic field and cryogenic requirements and high polarization with long spin relaxation times in low holding fields. The scattered neutrons and recoil protons will be detected in coincidence by two identical, large- area, position-sensitive detector arrays placed symmetrically to the left and right of the neutron beam. Each detector assembly consists of plastic and liquid scintillators and multi-wire proportional chambers, and will be sensitive to both neutrons and protons. Measurements of the opening angle and coplanarity of the detected nucleon pair will be used to dis­criminate against quasi-free n-p scattering from the heavier nuclei present in the polarized target.References1. A. Gersten, Phys. Rev. C 18, 2252 (1978).2. C.-Y. Cheung, E.M. Henley and G.A. Miller, Nucl. Phys. A305, 3^2 (1978).3. J. Button-Shafer, R.L. Lichti and W.H. Potter, Phys. Rev. Lett. 39, 677 (1977).DISCUSSIONvan OERS: Polarization reversal is achieved by reversing the holdingfield; does this cause problems in the precise determination of the scatteri ng angle?KNUTSON: No, the deviation of the outgoing protons in the magnetic fieldis less than one degree.Several people commented on other experimental details.8TEST OF CHARGE-SYMMETRY BREAKING IN THE n-p SYSTEML.G. Greeniaus Nuclear Research Centre, University of Alberta Edmonton, Alberta T6G 2N5Up to now violation of charge independence (CIB) has been estab­lished, but as yet no conclusive proof exists for charge-symmetry breaking (CSB) in the N-N system. However, certain polarization observables in the n-p elastic scattering system may yield results which depend on isospin non-conserving forces. At TRIUMF we plan to measure the difference AA = (Aoono"Aooon) between the neutron and proton analyzing powers at 500 MeV to a precision of ±0 .0 0 1.The CSB and CIB effects one hopes to measure are small, and the theoretical calculations are incomplete. La France et al.1 have calculated the contribution to AA from the one-photon exchange and the OPE amplitudes. In a different calculation including p-w mixing, Cheung and his collab­orators2 have also calculated AA. The results of these calculations are shown in Fig. 1. At larger angles where the calculations agree, the nuclear CSB effects are small but definitely measurable.Essentially the experiment is performed by determining left-right scattering asymmetries under all possible beam and target conditions. To reduce systematic errors both left and right scattered events should be detected in symmetric systems. Simultaneous use of a polarized beam and target may also cause difficulties. The quantity of interest is then the difference in scattering asymmetries with beam or target polarized [A = M A oono + Aooon)1•EB ” eT = A (pB“pT) + (pB+pT) • (0Equation (1) shows the major difficulty of the experiment: Pg and Pjmust be identically equal, or else known to high absolute precision if AA is to be extracted with an error of ±0.001. Since this is impracticalFig. 1 (a ). Predictions o f the difference in the analyzing powers from Ref. 1.% n (deg>Fig. 1(b) .  Contributions to CSB in np elastic  scattering at 460 MeV. The notation is  that o f Cheung (see contri­bution this workshop).A 0oon A oono210 MeV 420 MeV 610 MaV 730 MeV9Fig. 2. Layout fo r  the TRIUMF experiment on CSB in np elastic scattering.(error in Pb-Pt would b e ~ 0 .02), a simple solution is to do the measure­ment where A tsO. Many other sources of systematic error are proportional to A, making a crossover region even more attractive experimentally.There is a crossover point near 0c .m . ta 70°. The desired experimental precision of ±0.001 corresponds to a shift in the crossover angle of ±0 .05° in the lab.The proposed experimental layout is shown in Fig. 2 and a summary of properties is given in Table I. The neutron beam produced by scattering (polarized) protons in a LD2 target is incident on a large volume "frozen spin" polarized proton tar­get. Scattered neutrons are detected in position-sensitive detectors while the directions and ener­gies of the recoi1 protons are detected in multiwire propor­tional chamber-range counter telescopes. The neutron energy is determined by time of flight. The coincidence measurement allows the (n,np) back­ground to be reduced to less than 1% by using energy and angle kinematic constra i nts.A frozen spin target is used because large target volumes are pos­sible, and because a low holding field <2 kG is possible after the target- is polarized.A significant effort has been made to identify all potential errors and reduce their individual effects on AA to the 10-£t level. A summary of these errors is given in Table II.Table I. Experimental parameters.Beam energy 500 MeVProton angular range hl° < 0p < 57°Neutron angular range 27° < en < 37°Estimated angular resolutions ~0-5° (0 ) for bothproton and neutronEstimated Ta b l  resolution ~20 MeVVolume of frozen spin target i*0-50 cm3Neutron beam intensity 6 x l o 5 sec-1Estimated event rate h-S sec*1Estimated experimental precision |AA| < 0.001, |A6 0| < 0.05°10Table II. Summary of systematic errors.Cause of error Magni tude Effect on AAP+ * P-, 0L * eR P± = 0.6 ± 0.2 ~2 x 10'5|eL - eL| = 1° ~ 4  x 10_lt at A = 0.1Drift of proton beam across LD2 targetcorrelated with spin flip Ax = ±1 mm <4 x 10-1*Reproducibility of target position withrespect to the holding field |Ar| = +1 mm <4 x 10'“Incorrect precession of proton beam spin A<(> = 5° <io-uIncorrect precession of neutron beam spin A* = 5° ~10-5 at An = 0.1Correlation effect between hydrogen <10"1* for An = 0.1target polarization and residual neu­ Pn ~  0.035 r — ]tron beam polarizationeproj. =0-55°y y 1Multiple scattering in the target ~2  x 10'5Bending of paths of recoil protons inthe magnetic field of the target H = 5 kG ~2  x 10‘6Reproducibility of the holding field AH = +2.5 G <10-“Quasi-free scattering from target 0.5% background, ~1 x lO-1*material (carbon and oxygen) 101 subtraction errorNeutron detection stability 1% gain shift l!fc threshold2 x 10*uEnergy shift primary beam AE - 1 MeV <2 x 10'1*Shift in primary beam direction A0 = 0.1° <4 x 10'5The effect of quasi-elastic background is an important consideration. This was studied in a p-p elastic scattering experiment. Using opening angle, non-coplanarity and the energy sum constraints, it appears that background should be less than 0.5% in the np experiment. Beam motion or target position changes correlated with spin-flip cause systematic errors because of the rate of change of the n-p differential cross section with angle. Dynamic proton beam position control and reconstruction of the n-p scattering events will be used to control these errors. The stability of the neutron detectors will be monitored by measuring the average energy deposited in the counters by high energy passing protons as a function of time. Using this information final selection of events will be made off line and the effects of electronic drifts eliminated.Since the exact crossover angle is a poorly known function of the neutron beam energy we will eliminate this potential source of error by monitoring the mean primary proton beam energy to better than 0.5 MeV.As suggested by Table II, the list of potential problems in the ex­periment is impressive. Unfortunately, the list is also not static; but this is part of the joy of being an experimental physicist. It is planned to start data-taking in the fall of 19 8 2.References1. P. La France et al., preprint DPhPE 79-02, CEN, Saclay.2. E.M. Henley, private communication.DISCUSSIONSeveral people commented on the accuracy of background subtraction.GREENIAUS discussed the background expected in the planned (n,p) exper ment based on a (p ,p) test run performed in 1979- After cuts, the estimated background is less than 1/2%.12A TEST OF CHARGE SYMMETRY IN THE np->cko REACTION AT 795 MeVC.L. Hollas, C.R. Newsom and P.J. Riley The University of Texas, Austin, Texas 78712B.E. BonnerLos Alamos National Laboratory, Los Alamos, New Mexico 87545G . GlassTexas ASM University, College Station, Texas 77843The presence of a charge-symmetry-breaking force could be observed in the np-*dir° reaction as an asymmetric angular distribution about 90° in the center of mass, and has been discussed in detail by Cheung, Henley and Miller. 1 Hildebrand2 in 1952 made the first measurement for this reaction, and the most recent measurements are those of Bartlett et a t . 3 and of Wilson et at. ** Both of these recent measurements used a continuum neutron beam which can lead to problems in determining the correct center- of-mass angle associated with an event, which are especially evident in Wilson's data. At LAMPF, a nearly monokinetic neutron beam of high intensity has been developed5 using neutrons from pd-^ -Xn at zero degrees.We were able to obtain the proton beam chopped to ~40 nsec between pulses instead of the usual 5 nsec, so that time-of-f1 ight measurements could be used to select events initiated only by those neutrons in the peak near 1450 MeV/c.The experimental apparatus is shown in Fig. 1. The neutrons were collimated to a beam ~1 in. in diameter, swept of charged particles by Ml and struck a liquid hydrogen target. Recoiling charged particles were momentum analyzed by the MWPC spectrometer system. 6 Simultaneous measure­ments of the particles' flight time between scintillators SI and S2 enabled a rest mass calculation to be made (Fig. 2). Fewer than 0.1% of the events were incorrectly identified. A deuteron momentum spectrum binned from 0° to 4° is shown in Fig. 3. The peaks near 1550 and 850 MeV/c result from the np-^ di:0 deuterons emitted near 0° and 180° in the c.m. system. The large difference in size of the two peaks is unfor­tunately not due to a CSB effect, but rather due to the Jacobian which translates the c.m. cross sections into the laboratory. With four posi­tions of the spectrometer, we obtained the full angular distribution from 2° to 178° in 3° bin widths. The measured angular distribution is shown in Fig. 4 plotted against cos20c .m . The symbols V (A) are for data points less than (greater than) 90°. The solid curve represents a Legendre poly­nomial fit to the data including terms of the sixth order.The predictions for the angular asymmetry of Cheung, Henley and Miller1 at 577 MeV are shown in Cheung's paper in these proceedings (p.l). Also shown is the result of a calculation by Cheung7 at 800 MeV for the dominant term due to n~if° mixing, which can be parametrized in terms of odd-order Legendre polynomials as indicated in the figure. The presence of any CSB force would be manifest as an odd-order Legendre polynomial in the data. We performed least squares fit searches on the data illustrated in Fig. 4 using odd-order Legendre polynomials from 1 to 5- We also searched the data for the presence of the functional form describing the angular asymmetry from Cheung's calculation at 800 MeV, that is, the A1,13Fig. 1. The experimental apparatus used in the npmdm0 angular distribution measurement. Ml clears the neutron beam o f  charged par­t ic les ; LH2 is  the liquid hydrogen scatter­ing target; SI and S2 are thin scin tilla tors; VI, W2, W3, W4 are the multiwire proportional chambers; M2 is  the spectrometer magnet.500 1000 1500 2000Particle Mass (MeV)2500Fig. 2. The mass spectrum obtained with the spectrometer fo r  charged particles resulting from a ll incident neutron momenta. Protons and deuterons are un­ambiguously separated.Fig. 3. A deuteron momentum spectrum ob­tained near 4°. The two peaks near 850 and 1550 MeV/a resu lt from the npr+dn0 reaction  fo r  deuterons emitted near 180° and 0°, respectively  in  the center o f  mass. The deuterons between the two peaks resu lt from double p io n  p rod u c tio n .Fig. 4. The angular distribution for the np-*dv° reaction measured in the present ex­periment, plotted versus aos26a,m. with ®c.m. that o f  the deuteron. The symbol V(L)  is  for the center-of-mass angles less than (greater than) 90°. The solid  line repre­sents the 6th order Legendre polynomial f i t  which best describes the data.Fig. 5. The angular asymmetry for the np+dv0 reaction calculated by*Cheung"7 at 800 MeV. TVie asymmetry at 800 MeV may be parametrized in terms o f  Legendre polynomials as shown by Aofe; at the bottom o f the figure. 0crn(deg)jil*tA3 and A3 coefficients were held fixed at the values shown in Fig. 5 and the fitting parameter was a single normalization constant A^. We observe no statistically significant odd-order Legendre polynomial in the data.When the form for the asymmetry for n—MME mixing at 800 MeV is applied, weobtain A^ = -0 .8 18 ± 1 .6 0 2, where a value of +1 would indicate complete agreement. For the Afb parameter, we obtain values varying from +0.1*t ± 0.18% to -0.15 ± 0.50%. Cheung, Henley and Miller at 577 MeVcalculated Afb = 0.16%, while at 800 MeV Cheung's calculation indicates avalue of -0 .1 1 % due to the n-ir° mixing.We are forced to conclude that we observe no evidence for charge- symmetry-breaking forces in the np^-dn0 reaction to an order of 0 .50% in the integrated asymmetry parameter Afb- Most likely an experiment with an order of magnitude reduction in the statistical and systematic uncer­tainties will be required to directly observe charge-symmetry-breaking effects in this reaction.References1. C.-Y. Cheung, E.M. Henley and G.A. Miller, Nucl. Phys. A3**8, 365( 1980).2. R.H. Hildbrand, Phys. Rev. 89_, 1090 (1953)-3. D.F. Bartlett et at. , Phys. Rev. D J_, 198** (1970).**. S.S. Wilson et at., Nucl. Phys. B 3 3 , 253 (1971).5. C.W. Bjork et al., Phys. Lett. 63B, 31 (1976).6 . G. Glass et al., Phys. Rev. D 15, 36 (1977).7. C.-Y. Cheung, private communication (1979)•DISCUSSIONFRIAR: Could the experimental precision be improved by a factor of 10?HOLLAS: Very difficult, it is close to the limits of understanding of the systematics and related to the deuteron total reaction cross section.BONNER: It needs to be known to 1% to get a factor 10 improvement in thenp-3-dTr0 experiment.van OERS: Are any details known about the planned np->-dTr0 experiment atSIN by Ross 1e et al.BONNER: Plans are under way; expected precision is not known.15GENERAL DISCUSSION, SESSION IE.M. Henley provided a comparison of Gersten's and Cheung's calculations:GerstenDirect electromagnetic summedPWBAEffect of n-p mass difference in OPE = 6*np mass difference term in p-exchange (=6p) included, but no form factorSMOproduction included partially,via Im {6J }CheungDirect electromagnetic in a few partial waves (at large angle, look similar within an order of magnitude)DWBA= "6,not includedno Tr-production effectsThe curves resulting from the two calculations look very similar, except for the sign of 6^ and the discrepancy in the electromagnetic effect at smal1 angles.DAVISON: Quantify 'similar'?HENLEY: 10-20% (see graphs).COON: Some calculations of y + tt have been done but they disagree amongeach other.HENLEY: It is now known how to do it correctly.GERSTEN argued in favour of Yj parametrization, need up to Y 3•G. MILLER: Can the data fix 3 Yj's?KNUTSON: Presently planned experiments can yield at best one CSBparameter.BONNER: Are there other experiments than those currently planned thatshould be considered? (using newly available technologies)KNUTSON: Some CSB terms in old Wolfenstein work.GERSTEN has a list of observables affected by CSB [Phys. Rev. C 18, 2252(1978)].16 SESSION III HOI 2232 , HO I22U32 10 JAR3M3DCOMPARISONS OF 7i±d INTERACTIONS AND CHARGE-SYMMETRY BREAKING10 i I g  I uo f 63 a 'gnu s r lD  fane a 'n sJ a - ia D  To no aH sqm oo  6 b b b iv o iqGera Id A . MillerInstitute for Nuclear Theory and Department of Physics FM-15, University of Washington, Seattle, Washington 98195s i i 3 i Ion-srnoT 3091 s JosiiG bs; ■ 'A review of recent experiments1’2 and their theoretical interpreta­tion3 is presented. Charge-symmetry conservation requires the equality of elastic angular distributions for MMNO and ir--deuteron scatter­ing, as well as the equality of ir+- and ir”-deuteron cross sections. An important problem in the analysis of the data is a proper treatment and removal of effects of the Coulomb interaction between a pion and a proton.The first experiment to be discussed is the total cross-section measurement of Pedroni et a l.1 which covered a pion energy range of 70 to 370 MeV. After making corrections for effects of the Coulomb potential, these authors find energy-dependent differences of a few per cent between the tt+ and -rr-d cross sections. These effects are largest at about 1A0 MeV (a(ir-) —  0.91* a(ir+)) . The charge-symmetry violation can be parametrized in terms of mass and width differences between the A-isobars, in agreement with the ideas of Myhrer and Pilkuhn.3 Although the values of the ex­tracted mass and width differences are in agreement with the qualitative predictions of the quark model, there is a problem with the interpretation of the experiment. This occurs in the consideration of the ir-neutron interaction which is modified by the Coulomb field of the proton. Two different groups1’3 disagree on the sign of this effect. Indeed, if Pedroni et al. had used the correction formula of Myhrer and Pilkuhn, the charge-symmetry breaking effects would be reduced in magnitude by a factor of two (for pion energies less than about 200 MeV).The second experiment to be discussed is the recent angular distribu­tion measurement of Masterson et al.3 Data were taken at 1^3 MeV, and a second study at 240 MeV is in progress. This experiment provides an impor­tant check on the interpretation of the experiment of Pedroni et a l. If their A-mass difference idea is correct, then at 1^3 MeV and at forward angles, where the impulse (or single scattering) approximation is valid, the angular distributions for -rr+ and it- scattering should have the same shape, and the tt" differential cross section should be only 9**% of the tt+ differential cross section. (This is true for Coulomb-corrected angular distributions.) However, the data show no evidence for charge-symmetry breaking. The results of the 2h0 MeV measurement should prove very inter­esting because Coulomb effects, which complicate especially the Pedroni et al. measurement, are expected to be smaller1*3 than at 1^3 MeV.References1. E. Pedroni, K. Gabathuler, J.J. Domingo, W. Hirt, P. Schwaller,J. Arvieux, C.H.Q. Ingram, P. Gretillat, J. Piffaretti, N.W. Tannerand C. Wilkin, Nucl. Phys. A300, 321 (1978).2. T.G. Masterson, J.J. Kraushaar, D.A. Lind, R.J. Peterson, R.S.Raymond, R.A. Ristinen, R.L. Boudrie, N.S.P. King and E.F. Gibson, these proceedings, p. 18, and Bull. Am. Phys. Soc. 26^ 581 (1981).3. F. Myhrer and H. Pilkuhn, Z. Phys. A276, 29 (1976).17DISCUSSIONMEASDAY: Is the charge radius of the pion important in calculations ofSMFd and, in fact, is the strong interaction well enough understood to get reliable results?G. MILLER: The charge radius of the pion was taken into account. Weused rc = 0.64 fm for the pion and folded it together with the proton charge radius for which we used rc = 0.80 fm. As far as the strong inter­action goes, it is well enough known to give good results at forward angles.van OERS: In your calculations you assume that the centre of mass andcentre of charge of the deuteron coincide. Could there not be a polariza­tion of the deuteron due to the different Coulomb interactions between the proton and the positive and negative pions?G. MILLER: I expect this is a second-order effect.PREEDOM: Is the time scale in n^d scattering too short for polarizationto occur?G. MILLER: I can't comment on that. Certainly everyone ignores that kindof polarization.FRIAR: There is one group that treats the deuteron as an elementaryparticle.G. MILLER: Theorists need to review all these calculations and do thembetter. If we simply take a (Tr"d) -a (ir+d) without electromagnetic correc­tions, we find a cross-section difference of -3.6 mb. Pedroni calculates Coulomb corrections of -6.4 mb while Myhrer and Pilkuhn find -1.7 mb.PREEDOM: Thomas used a relativistic Schrodinger equation in his work.Would it make much difference to use the Klein-Gordon equation?G. MILLER: The effects are not major.18CHARGE SYMMETRY AND THE t^d INTERACTIONT.G. Masterson, J.J. Kraushaar, D.A. Lind, R.J. Peterson, R.S. Raymond and R.A. Ristinen University of Colorado, Boulder, Colorado 80302R.L. Boudrie and N.S.P. King Los Alamos Scientific Laboratory, Los Alamos, New Mexico 875^5E.F. GibsonCalifornia State University, Sacramento, California 95819The comparison of ir+d and ir~d differential cross sections is a very sensitive test of charge symmetry. We have made accurate differential cross-section measurements of u+d and ir“d elastic scattering at 1^3 MeV at LAMPF (EPICS). Differential cross sections for tt±p elastic scattering were also measured at the same time, and absolute normalizations were ob­tained by comparing with ir±p phase-shift calculations and the tr-^p elastic scattering data of Bussey et al. 1 at the same energy.Our ir+d differential cross sections agree well with ir+d measurements of Gabathuler et al.2 at the same energy and with ir+d three-body Faddeev calculations of Giraud et al . 3 There have been no previous accurate measurements of i\~d differential cross sections in this energy region.Our preliminary ir+d and ir“d differential cross sections are shown in Fig. 1. The theoretical curves are three-body Faddeev calculations of Thomas4 which include all S- and P-wave pion-nucleon amplitudes, a realis­tic deuteron wave function and no absorption. Charge symmetry is assumed in this calculation.The ratio method of comparing ir+ and ir" differential cross sections has allowed us to make a very sensitive test of charge symmetry by elimi­nating many experimental and theoretical uncertainties. Preliminary data comparing the difference of ir_d and ir+d differential cross sections with the sum of tr“d and tr+d cross sections are shown in Fig. 2. The errors are statistical only. The data have not been corrected for any CoulombFig. 1. Preliminary t^±c? elastic  scattering cross sections at T-„ = 142 MeV. The vd phase shifts used in the calculations are from Thomas and include a ll S - and P-wave vN amplitudes.They assume charge symmetry but incorporate Coulomb differences appropriate for r+d and r.~d scattering, respectively.40 60 80 100 120 140^c.m.Masterson et al. (EPICS)_______ I_________ I_________ L77" *-0“i------ 1------ 1------ 1—PRELIMINARY  Preferred 19 9 Only 6.7 % D  state Absorption19Fig. 2. Preliminary it±d differences. The data represent the difference between n~d and tt +d elastic  scattering differential cross sections divided by the sum. Errors are sta tistica l. No Coulomb corrections have been made. The theoretical calculations were done by Masterson and Thomas and represent the purely Coulomb differences expected between it~d cross sections for  various sets o f  three-body nd phase sh ifts. The ’preferred ' set includes a ll S - and P-wave t tN amplitudes, 4% D state in the deuteron and no absorption. The '6.7% D’ and 'absorption' sets change the preferred set by including 6. 7% D state in the deuteron and pion absorption, respec­tive ly , while the 'P 3 3  only’ set includes only the P3 3  ttW amplitude. A ll calculations assume charge symmetry.effects. A comparison is made (with the assistance of A.W. Thomas'*) with several three-body ird calculations which isolate Coulomb and Coulomb nuc­lear interference effects from the cross section while explicitly assuming charge symmetry. The envelope of theoretical curves therefore represents charge-symmetry conservation. The deviation of our data points from these curves is equivalent to a possible violation of nuclear charge symmetry.References1. P.J. Bussey et al., Nucl. Phys. B58, 363 (1973).2. K. Gabathuler et al. , Nucl. Phys. A350, 253 (1980).3. N. Giraud, C. Fayard and G.H. Lamont, Phys. Rev. C 21, 1959 (1980). h. A.W. Thomas, private communication.20PROPOSED MEASUREMENT OF THE REACTION d + d -v MME + ‘♦He BY THE NEUCHATEL- GRENOBLE-SACLAY-ORSAY-SOUTH CAROLINA COLLABORATIONB.M. PreedomDepartment of Physics, University of South Carolina,Columbia, South Carolina 29208The reaction d + d ■* ir° + '♦He provides a very good test of the validity of charge symmetry.1 It is forbidden hadronically unless it pro­ceeds via virtual n° production and ir-p mixing or via a T = 1 component in the ‘♦He ground state. Upper limits for this reaction have been set at JI NR2 (<900 pb/sr at 404 MeV), Berkeley3 (<97 pb/sr at 460 MeV), and at Saclay^ (<19 pb/sr at 787 MeV) . Comparing with a calculation of Greider,5 which uses an impulse approximation ignoring isospin, the latter limit sets charge-symmetry conservation >99*73%. Our proposed experiment at SATURNE will push the sensitivity of the measurement to at least two orders of magnitude below the present upper limit. The cross section at this level (0.1 pb/sr) is comparable by virtual photoproduction. This estimate is the average of that obtained by reducing Greider's calculation by two EM vertices (0.5 pb/sr) and that obtained by reducing the empirical cross section for d + d y + ‘♦He by one EM vertex (0.04 pb/sr).The proposed experiment will use the SPES I beam line and spectrom­eter together as a single 11 He-spectrometer at 0° with dE/dx information obtained at the intermediate and final focus and time of flight through the last element. A test run has proven that this method can unambiguous­ly identify a-particles. In order to reduce the background from necessary contaminants such as the walls of the liquid D2 target, we plan to measure the ‘♦He in coincidence with the ir° produced at the target. The shielding for the ‘♦He detectors is provided by the shielding for the experimental cave.References1. E.M. Henley, in Isospin in Nuclear Physics, ed. D.H. Wilkinson (North-Holi and, Amsterdam, 1969), p* 15, and in High-Energy Physics and Nuc­lear Structure, ed. G. Tibell (North-Hol1 and, Amsterdam, 1974), p. 22.2. Yu.K. Akimov et al. , Sov. Phys. JETP ]_4, 512 (1962).3. J.A. Poirier and M. Pripstein, Phys. Rev. 122, 1917 (1961) and Phys.Rev. U0, 1171 (1963).4. J. Banaigs et at. , Phys. Lett. 53B, 390 (1974).5. K.R. Greider, Phys. Rev. 122, 1919 (1961).21DISCUSSIONCHEUNG: The reaction mechanism in which the n° is produced by a y in thefinal state is probably not important.HENLEY: I expect that if MME 1 s are produced via a y intermediary, the y'sthemselves will be produced through interactions between the deuterons; something like d + d-*-d + d +  y->- ‘♦He + ir°. There are also some data for n° mechanism.CHEUNG: I am currently trying to improve calculations for the dd -* air0reaction using a two-nucleon mechanism.HENLEY: The "back-of-the-envelope" calculations used to estimate thedd air0 cross section are likely too high by a factor of roughly ir2 . In addition, there are likely to be other symmetries which will tend to further reduce the cross section.van OERS: How well will your ii I  detector work in the background of theexperimental hall?PREEDOM: There will not be much background at backward angles. Ourdetector will consist of blocks of lead glass disposed around the beamline in a square array. By requiring a coincidence between the two y-raysemitted by ir°, the random background is made very small.van OERS: Can you proceed without a ir° detector?PREEDOM: No. Although the system is very clean for a-particles, there isstill enough a background to swamp a signal from dd -»■ air at the 0.1 pb1evel .van OERS: When do you expect to be able to carry out the experiment?PREEDOM: The earliest we can have everything ready is the summer of 1982. I expect that the experiment will actually run in the fall of 1982.22CHARGE ASYMMETRY IN THE A=2 AND A=3 NUCLEAR SYSTEMSSidney A. CoonDepartment of Physics, University of Arizona, Tucson, Arizona 85721In this remark I collect predictions of the charge asymmetry in the T=1,£=0 partial wave of the NN interaction. The predictions are from various meson-exchange models. The compilation can be compared with re­cently determined effective range parametersir”d -+ ynn |ann| = 18.6 ± 0.5 fm rnn = 2.83 ± 0.16 fm (Ref. 1)nd ■+ pnn rnn = 2.69 ± 0.27 fm (Ref. 2)nd ->- pnn |annl = 16-9 ± 0.6 fm rnn = 2.65 ± 0.18 fm (Ref. 3) •If we accept the usual subtraction of the direct electromagnetic contribu­tion to |a^pm  ^| = 7.828 ± 0.008 fm and |r^®^ | = 2 .80 ± 0.02 fm, the purely nuclear effective range parameters become | V I  - 17.1 ± 0 .2 fm and "rpp" = 2.84 ± 0.03 fm (see, however, Sauer and Walliser4). Then the charge asymmetry shows itself in the quantities Aa = |ann| - |"app"| andA r  =  r - " r  11nr rnn rpp ■Among the T=1 partial waves, which are alone responsible for the 3He-3H binding energy difference, the 1Sq state makes up 90% of the three- nucleon bound state. Therefore, removal of the direct e.m. contribution, recently determined5 to be 683 ± 29 keV, from the binding energy differ­ence of 76** keV, yields a third number AE = 81 ± 29 keV, which also characterizes the charge asymmetry in the T=1,£=0 state.Of these "experimental" numbers,Aa A  1.5 ± 0.5 fm Ar «  -0.01 ±0.11 fm AE = +81 ± 29 keVAr «  -0.15 ± 0.27 fm "Aa «-0.2 ± 0.6 fm Ar ~  —0.19 ± 0. 18 fm " ;the positive Aa from the MMCd capture experiment agrees with AE, both im­plying that the 3So nn interaction is slightly more attractive than the pp one.The following predictions for Aa and Ar were made by adding a model for AV = Vnn-Vpp to the charge symmetric Reid soft core (RSC) potential and interpreting the change in the low energy parameters from those of the RSC alone as Aa = |ann| - |"app"|, etc. The contributions of the AV to AE were estimated in the same "model-independent" manner used for the direct e.m. contributions. I made all the calculations except those marked with an asterisk; they were made by the proposers of that charge asymmetric potential.I note that pui mixing is the only significant process with some agreement between authors, and that the sum of irq mixing and pm mixing appears consistent with the "experimental" Aa, Ar and AE of Refs. 1 and 5- It is interesting to compare this result with the charge asymmetry in the AN interaction where the analogous term from J(He-)(H binding energy differ­ence is ILT «  350 keV. Particle mixing models (EA, trn, ptu, etc.) can ac­count for the spin-singlet AN charge asymmetry, but apparently the spin- triplet prediction does not agree with experiment.1523Conference, Eugene, August 1980, Vol. I, p.222.2. H. Gurutzsch et al. , Nucl. Phys. A3A2, 239 (1980); ibid., p. 199.3. W. von Witsch et al., Nucl. Phys. A329, 141 (1979); Phys. Lett. 91B,3**2 (1980) ; ibid. , p. 207.4. P.U. Sauer and H. Walliser, J. Phys. G: Nucl. Phys. 3, 1513 (1977).5. R.A. Brandenburg, S.A. Coon and P.U. Sauer, Nucl. Phys. A294, 305 (1978).6. M. St.J. Stevens, Phys. Lett. J_9_, 499 (1965).7. L.K. Morrison, Ann. Phys. 50^ , 6 (1968). Morrison's three potentials are based on, in descending order, Feynman diagrams, dispersion rela­tions and sum rules.8. D.O. Riska and Y.H. Chu, Nucl. Phys. A235_, 499 (1974).9- M. Chemtob, in Interaction studies in nuclei, eds. H. Jochim andB. Ziegler (North-Hol1 and, Amsterdam, 1975), p. 487.10. S. Furui, Nucl. Phys. A2J74, 370 (1975).11. M.K. Banerjee, Univ. of Maryland preprint 75-050, 1975 (unpublished).12. T.B. Wells, dissertation, Univ. of Maryland, 1978 (unpublished).13- P.C. McNamee, M.D. Scadron and S.A. Coon, Nucl. Phys. A249, 483 (1975).14. S.A. Coon, M.D. Scadron and P.C. McNamee, Nucl. Phys. A287, 381 (1977).15. J.L. Friar and B.F. Gibson, Phys. Rev. C \1_, 1752 (1978]T“16. S.A. Coon and P.C. McNamee, Nucl. Phys. A322, 267 (1979); S.A. Coon,Nukleonika 25, 594 (1980) .Charge Asymmetric Process Reference Aa Ar AE(fm) (fm) (keV)Charge asymmetry of irNN Stevens6 +0.111 -0.001 + 5coupling constant Morrison7 +0.222 -0.001 + 9Morrison7 -0.456 +0.003 “19Charge dependence of Morrison7 -0.805 +0.005 “35nucleon masses in inter­mediate states:Tr+ir" exchange Riska and -1.914 +0.040 -138t t° t t0  exchange Chu8 -0.600 +0.011 -44yir0 exchange:NN intermediate states BS method Riska-Chu8 +0.211 -0.006 +14AA intermediate states static Chemtob9 +0.17* -0.003* +34AA intermediate states static Furui10 -0.14 to ... ...g ii I  exchange B1 ankenbec 1 er- 0.88Sugar method:NN intermediate states Banerjee11 +1.31* ... ...NA intermediate states static Wells12 -0.12* ... ...AA intermediate states static Wells12 0.0 * ... ...ir0ri mixing McNamee +0.06 -0.008 +17n . . et al.13p°u) mixi ng:local part only Coon et al}h +0.74 -0.014 +56local + nonlocal parts Friar-Gibson15 +0.87* -0.018* ...References1. B. Gabioud et al., SIN preprint (1980), and Proc. 9th Int. Few Body2*tDISCUSSIONFRIAR: The pto coupling constants you use are larger than the usual exper­imental numbers. Where did you get these values?COON: Let me emphasize the mixing parameters. The numbers come from twosources: a) photoproduction of p and w in which you try to look forinterferences, and b) from e+e" from Orsay. This is a very clean experi­ment. I prefer to throw away other data even though they ostensibly have smaller error bars.van OERS: What about using other mirror nuclei with A > 3?COON: This is very difficult. If A > 3 you cannot use Friar's symmetryprinciple to eliminate geometric effects. The result is that your results are model dependent, especially as regards core polarization. In addi­tion, as you go to heavier nuclei, you must use higher partial waves and the calculations become unmanageable.van OERS to G. Miller: What accuracy is required of the EPICS experiment?G. MILLER: They require an accuracy of <0.5%. However, even the presentresult is interesting because it disagrees with the SIN result for Aa = a(ir+d) - a(Tr"d) (total cross sections). The latter would require the EPICS result to be <0 while it is observed to be >0.van OERS: Do you mean that the elastic ir±d scattering is already accurateenough?G. MILLER: No! Remember that there are large electromagnetic correctionsto Aa. Suppose that Pedroni's calculation for the electromagnetic effects is too large; this would greatly change the picture. We still need better data here and the first thing is to make sure the MM4 angular distributions are correct.HOLLAS: What do you feel the chances are that the Coulomb corrections arewrong?FRIAR: Not negligible! The long wavelength part of the photon exchangeis well calculated and is based on very good principles. The short wave­length part, however, is based on models and is not well understood atall .van OERS: Does everyone agree that the uncertainties in ann, anp and appare as large as Dr. Coon has suggested?COON: These large uncertainties do not include restrictions due to e“dscattering. You can reduce the uncertainty if you assume that any scat­tering lengths yielding a deuteron wave function in disagreement with e"d data are to be rejected. In addition, I should say that Sauer, in his calculation of the scattering lengths, allowed complete freedom to the phase shifts. Most people would feel, however, that and 3S1 are not completely independent.25van OERS: Is there more to be learned from the effective ranges?COON: I don't know. Sauer did not consider them.HENLEY: What about experimental scattering length uncertainties?van OERS: The small uncertainty in ann is primarily due to the last ex­periment performed.HENLEY: I am not sure I believe the error of only ±0.6 fm on ann.van OERS: The value of ann usually quoted is the result of averaging many measurements.HENLEY: As it stands, the experimental error on ann is really no betterthan the theoretical uncertainty.McDONALD: Are there other experiments or observables that are sensitiveto CSB?GERSTEN: Yes. I have already put together such a list.BONNER: The normalization of all cross sections measured with neutrons atLAMPF depend on a factor , .g(pp -> dn^Jn a(np d iT 0 )which is taken to be exactly 2. How accurately do you need to measure the deviation of n from 2 in order to probe for CIB?in-in r-w -r, a(pd -* 3HeTr°) . . r ..HENLEY: The ratio g (p(j fir0)  ma^ 9 1 ve some information on CIB.COON: The calculation in which n = 2 was derived is old and relativelycrude. Is it important to experimentalists that it be redone?BONNER: It would be nice to have it redone because its value is assumedin the normalization of all neutron cross-section data. It may be signi­ficant that Arndt usually finds it necessary to renormalize neutron beam results by about 8%.HENLEY: My feeling is that the value of n could well be in error by 10%.van OERS: We recently received from VerWest some diagrams showing crosssections for pp -*• d-rr+ and np -*■ d-rr0 . They differ by very close to a factor 2 suggesting that n does not deviate from 2 by a large amount.BONNER: What about np -*■ dir0? Are there other useful observables, forinstance using a polarized neutron beam?HENLEY: Polarization observables might well be more sensitive to CSBbecause the potentials responsible are spin dependent.CHEUNG: Is it hard to measure the polarization of the deuteron?BONNER: Yes.HENLEY: Suppose you look at np -*■ dir0 and measure the deuteron asymmetry.CHEUNG: You no longer have symmetry about 90° even in the absence of CSB.BONNER: Right, but what are, in fact, the effects of CSB on the deuteron asymmetry and other polarization observables?van OERS: I think this discussion emphasizes that theorists should alwayscalculate all spin observables.EVENING DISCUSSION SESSION: THEORYBONNER: Is there any way to decide what experiment (of the small numberof possible ones) is the best one to do?COON: We need clean experiments on particle-particle interactions, e.g.MSOMM mixing.BONNER: What about NN experiments - are there any that need to be done?BIRCHALL: Measurements of spin-correlation parameters.BONNER: Theorists should report predictions of the amplitude 4>g, withclear normalizations.CHEUNG: Theory should fit both cross sections and polarizations inir-product i on.UNIDENTIFIED: At what energies should the calculations be done?GIBSON: At those available at existing experimental facilities: 200, 500,800 MeV.GREENIAUS: Is measurement of scattering asymmetry in np -»■ dir0 withpolarized protons a useful experiment?CHEUNG: No. CS does not imply any symmetry.UNDENTIFIED: What about measuring deuteron polarization in np dir0?CHEUNG: This needs to be calculated.UNIDENTIFIED: Are ir+t 3HeiT0 and ir-3He ■* tir° analogue experiments useful?UNIDENTIFIED: Nuclear structure uncertainty may mask any observableeffect; it contains no better information than T7±d X.UNIDENTIFIED: The Coulomb aspects of MMYd need to be examined.FRIAR: That is very hard, one needs to introduce radiative corrections tothe strong interactions.PREEDOM: What about n_production? i\~p -*■ n°n?UNIDENTIFIED: CSB will be a very small part of that.FRIAR: What is the experimental situation i n n -*■ 3tt?COON: Have been told that it is huge.PREEDOM: We want a definitive theoretical discussion of scattering lengthsand effective ranges; are there real ann-app differences, what are the best known values?2728COON: If you assume the strong interaction is a local one, you can get anunequivocal extraction of the electromagnetic part of app . However,P. Sauer has studied non-locality of :UU inside 1 fm and finds that huge variations in app can be obtained from non-local unitary transformations. He claims pursuit of ann=app is a pointless task.GIBSON and COON said it is not; Sauer's calculations need to be re­examined. Additional physical constraints can be imposed on the variation in :UU inside 1 fm, such as the deuteron wave function.PREEDOM reiterated the pleas from his talk. (See recommendation No. 7•)[The editors regret that from notes on this discussion session it was not possible to identify some of the speakers and thus offer their apologies to those who must remain anonymous in these proceedings.]29EVENING DISCUSSION SESSION: EXPERIMENTAn initial question was posed by W.J. McDonald to the entire group:Are experimental accuracies currently sufficient to provide a rigorous test of theory? In particular, what is the general feeling about the cur­rent limits on the accuracy of theoretical predictions of CSB and what are the expected accuracies in the current generation of experiments?A general consensus was:a) Theory is accurate to ~±3 x 10-3.b) Experiment can probably reach ~±1 x 10“3.c) The important thing for the upcoming experiments is to establishthe existence of CSB beyond direct electromagnetic effects.d) The current experiments will not define the mechanism of CSB. Detailed discussion followed.KNUTSON: Are nuclear phase shifts well enough known at 500 MeV to allowgood predictions to be made?van OERS: Yes.GERSTEN: I am not so sure. I do trust Arndt's analysis more than Lehar's,but there are still uncertainties.van OERS: The uncertainties which appear in the phases are not largeenough to affect asymmetry due to CSB to the level observable in the pro­posed experiments.McDONALD: Are the predicted differences in the asymmetries in np scatter­ing really different at 200 and 500 MeV so that measurements at these two energies are complementary in unravelling the direct electromagnetic and more interesting CSB effects?G. M I LLER:  Yes .van OERS: What about 800 MeV?G. MILLER and GERSTEN: This is not clear.van OERS: What should be done next, both experimentally and theoretically?G. MILLER: If experimental results in np elastic scattering deviate sig­nificantly from what is due to direct electromagnetic effects, then angular distribution data would be very desirable.C. MILLER: Is there any point in checking the Schwinger scattering termat smal1 angles?30GERSTEN: Perhaps, if it can be measured very accurately {±2%).G. MILLER: I have faith in the Schwinger term.KNUTSON: The Schwinger term has already been very accurately measured -some argument.KNUTSON: The np -* dir0 experiment as currently carried out by observinga(e) - a(ir-0) for the deuterons seems hopeless. It seems very difficult to improve this experiment sufficiently to make it yield a clear signature for CSB.van OERS: Someone contemplating a new measurement must get uncertaintiesin the fore-aft asymmetry below 0.05%. This is very difficult.KNUTSON: Are there any symmetry principles which have direct bearing onthe polarization observables in np -> dir0?G. MILLER: One might compare pn -*■ d i r 0  and pp -* d iT + . Under charge inde­pendence, the deuteron asymmetries in the two reactions should be the same at al1 angles.van OERS: Does the following measurement work:np -> dir0-v at the zero crossing?np ->• dir0C. MILLER: Is measuring the deuteron vector polarization worth while?BONNER: We will attempt to measure the deuteron vector polarization inthe pp -*■ VMMN reaction this summer.C. MILLER: Is there not an angle at which the deuteron asymmetry innp -* dir0 goes through zero?BONNER: It would be useful to calculate the magnitude of the deuteron asymmetries in np -> dir0 and np dir0 . At high energies the asymmetry never goes through zero, but it does at TRIUMF energies.ROY: We can now prepare target and projectile spins in any direction.Are there more sensitive observables?GERSTEN: Is it experimentally reasonable to use n or p in a study ofnp -* diT0?McDONALD: We need an indication of the magnitude of expected CSB effects before it is possible to say whether or not the experiment is feasible.BONNER: Given the helicity amplitudes for CSB (<J)6) , it should be easy tocalculate other observables. Theoreticians can calculate <J>6 , and <(>■[. ..4)5 are found from phase-shift analyses. Then other observables can be calcu­lated easily.GERSTEN: We can do this.31van OERS: The next experiment to look at in np elastic scattering is thedifference between Axz and Azx. This is a hard experiment since the mag­netic field of the polarized target has a different orientation in the two parts of the experiment.KNUTSON: We already have the y's so the CSB effects can be calculated.van OERS: It would be good to calculate the effect of CSB on otherdeuteron observables.ROY: The next level of difficulty in experiments is to measure the pola­rization of the outgoing particles.BONNER: This requires more complicated calculations. The pp -* cfir+ experi­ment will tell us about the strong interaction.van OERS: On another subject, there will be difficulties in analysingdd -*■ air0 due to the reaction mechanism, will there not?G. MILLER: If, experimentally, any MMERB at all are seen, we have CSB.However, we will not know if it is due to a T = 1 component in ^He or due to CSB in the reaction mechanism. The deuteron really is T = 0 because the only way to have T = 1 is to have parity violation as well. The ^He might conceivably have a small T = 1 component. The dd -+■ air0 reaction is indeed very complicated; any SM production is always difficult. Neverthe­less, we can probably say something.BONNER: Reactions involving more than two nucleons are always difficultto interpret. We don't know if CSB occurs in the reaction mechanism, or in the a-particle, i.e. complex nucleus.C. MILLER: Is there any reason to look at ir*??G. MILLER: It is not clear if these reactions are particularly sensitiveto CSB. There might be a polarizing Coulomb effect in SMYV due to changing the pion charge.BONNER: To summarize, it would seem that a comparison of np and njjelastic scattering is the best experiment to look at now.GIBSON: It must also be emphasized that no one experiment will be defini­tive. At least, we need np elastic at two energies.32RECOMMENDATIONS1. The experiment currently most likely to provide definitive evidence for the existence of charge-symmetry breaking is np elastic scattering in which one or both of n and p is polar­ized perpendicular to the scattering plane and the analyzing power is observed.2. Since no one experiment will enable disentangling of the various contributions to charge-symmetry breaking, np elastic scattering should be carried out at two or more energies.The planned experiments at TRIUMF and IUCF are thus comple­mentary.3. Future reports on charge-symmetry-breaking calculations for NN scattering should tabulate the helicity amplitude <(>6 •4. Future reports on charge-symmetry-breaking calculations for reactions other than elastic scattering should include results for all polarization variables.5- P. Sauer's analysis of extraction of direct electromagnetic corrections with different transformations of the short-range part of :UU needs to be redone, imposing additional physical constraints (e.g., the deuteron wave function) on the permitted transformations.6. In the -rr+d and MMOd systems Coulomb corrections need to be better calculated.7. For dd -* a i r 0 , (a) can anyone do realistic calculations of angular distributions using the virtual photoproduction mech­anism, and (b) are there symmetry arguments leading todo (0) _ n ?dft33WORKSHOP PARTICIPANTSR. ABEGG, TRIUMF, Vancouver, British Columbia V6T 2A3 J. BIRCHALL, University of Manitoba, Winnipeg, Manitoba R3T 2N2B.E. BONNER, Los Alamos National Laboratory, Los Alamos, New Mexico 875^5C.-Y. CHEUNG, Carnegie-Mel Ion University, Pittsburgh, Pennsylvania 15213H.E. CONZETT, Lawrence Berkeley Laboratory, Berkeley, California 9^*720S.A. COON, University of Arizona, Tucson, Arizona 85721C.A. DAVIS, University of Alberta, Edmonton, Alberta T6G 2J1N.E. DAVISON, University of Manitoba, Winnipeg, Manitoba R3T 2N2H.W. FEARING, TRIUMF, Vancouver, British Columbia V6T 2A3J.L. FRIAR, Los Alamos National Laboratory, Los Alamos, New Mexico 875^5A. GERSTEN, University of British Columbia, Vancouver, B.C. V6T 2A6B.F. GIBSON, Department of Energy, Washington, D.C. 205^5J.M. GREBEN, University of Alberta, Edmonton, Alberta T6G 2J1L.G. GREENIAUS, University of Alberta, Edmonton, Alberta T6G 2N5H.P. GUBLER, University of Manitoba, Winnipeg, Manitoba R3T 2N2R. HELMER, Simon Fraser University, Burnaby, British Columbia V5A 1S6E.M. HENLEY, University of Washington, Seattle, Washington 98195C.L. HOLLAS, University of Texas, Austin, Texas 78712D.A. HUTCHEON, TRIUMF, Vancouver, British Columbia V6T 2A3 K.P. JACKSON, TRIUMF, Vancouver, British Columbia V6T 2A3W.W. JACOBS, Indiana University Cyclotron Facility, Bloomington, Indiana 47^01L.D. KNUTSON, University of Wisconsin, Madison, Wisconsin 53706W.J. McDONALD, University of Alberta, Edmonton, Alberta T6G 2J1D.F. MEASDAY, University of British Columbia, Vancouver, B.C. V6T 2A6C.A. MILLER, TRIUMF, Vancouver, British Columbia V6T 2A3G.A. MILLER, University of Washington, Seattle, Washington 98195G.A. MOSS, University of Alberta, Edmonton, Alberta T6G 2J 1B.M. PREEDOM, University of South Carolina, Columbia, South Carolina 29208G. ROY, University of Alberta, Edmonton, Alberta T6G 2J1J.T. SAMPLE, TRIUMF, Vancouver, British Columbia V6T 2A3J. S0UKUP, University of Alberta, Edmonton, Alberta T6G 2J1J.G. S0WINSKI, University of Wisconsin, Madison, Wisconsin 53706J.P. SVENNE, University of Manitoba, Winnipeg, Manitoba R3T 2N2S. THEBERGE, University of British Columbia, Vancouver, B.C. V6T 2A6J. UEGAKI, University of Alberta, Edmonton, Alberta T6G 2J 1W.T.H. van OERS, University of Manitoba, Winnipeg, Manitoba R3T 2N2

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