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Huber, Garth Murray

TRIUMF

Proton induced pion production has been investigated in a series of experiments using the Medium Resolution Spectrometer at TRIUMF. Data were obtained for the ⁷Li(p̄, π⁺)⁸Li*, ¹²C(p, π⁺)¹³C*, ¹³C(p, π⁻)¹⁴O*, ¹³C(p, π⁺)¹⁴C*, and ¹⁶O(p̄, π⁺)¹⁷O* reactions at Tp = 250 , 354 and 489 MeV, and are compared with previously published results taken at other energies above and below the ∆₁₂₃₂ resonance region. Because the signatures of the ∆₁₂₃₂ resonance should be the least ambiguous in this energy range, theoretical calculations which include ∆₁₂₃₂ degrees of freedom should be able to describe these results, if they are to have any hope at describing the experimental situation at all. At fixed four-momentum transfers squared of t > 0.45 GeV²/c², the (p, π⁺) differential cross sections exhibit a maximum near the invariant mass of the ∆₁₂₃₂. This energy dependence is similar to that shown by the pp → dπ⁺ reaction at equivalent center of mass energy and four-momentum transfer squared, and thus it provides strong evidence of a NN →NNπ⁺ process in the (p, π⁺) reaction mechanism. Unlike the (p, π⁺) reactions, the differential cross sections of the (p, π⁻) reactions decrease with increasing energy through this region. This difference is consistent with an interpretation of the (p, π⁻) reaction mechanism as a NN → NN π⁻ process in which non-resonant amplitudes are dominant in this region. Analyzing power angular distributions for many states of the ⁷Li(p̄, π⁺)⁸Li* and ¹⁶O(p̄, π⁺)¹⁷O* reactions exhibit broad similarities with those of the p̄p → dπ⁺ reaction. Interpretation of this trend is complicated by other analyzing power angular distributions which have entirely different shapes. Data were also obtained for the inclusive pion production reactions to the continuum. Double differential cross sections display an energy dependence similar to that of the pp → dπ⁺ reaction, and analyzing power angular distributions are similar to those of the p̄p → dπ⁺ reaction. This is consistent with earlier interpretations of a quasi-free NN → NNπ⁺ process occurring within the nuclear environment. Theoretical calculations have been performed for two of the exclusive reactions studied in this work. A resonant two nucleon model, and a relativistic stripping model using a ∆-hole potential, both do a better job of describing the differential cross section data at the ∆₁₂₃₂ invariant mass than at lower energies. Both calculations can only be said to qualitatively describe the broad features of the analyzing power data. Thus, the results presented in this thesis indicate that there are some effects of the ∆₁₂₃₂ resonance in the (p, π⁺) reaction, but that these effects are less clear in the (p, π⁻) reaction.

Text

2019-03-06

Attribution-NonCommercial-NoDerivatives 4.0 International

http://hdl.handle.net/2429/68500

Unreviewed

http://creativecommons.org/licenses/by-nc-nd/4.0/