Pion Production on Nuclei

Abstract

To characterize the experimental situation on π production on complex nuclei in a few words, one might say that while more experiments certainly are needed if one wishes to understand the details of the reaction mechanism, the quality of the experiments is better and the number of cases studied larger than in some other important areas of pion-nuclear physics. This has, above all, come about through the efforts of the Uppsala [1–3] group, that has studied (P,π⁺) and (p,π⁻) reactions on a number of targets (⁹Be, ¹⁰B, ¹²C, ¹³C, ¹⁶O, ²⁸Si and ⁴⁰Ca for π⁺, ⁹Be and ¹³C for π⁻) at 185 MeV incident proton energy. What makes these experiments so important is first of all the fact that the angular distributions have been measured, with rather high accuracy (at least in the π⁺ case); furthermore, it has been possible to separate the cross sections leading to the various states of the final nucleus, as long as these states are not too closely spaced. Generally speaking, the results of these experiments are that a) the cross section for π⁺ production is much larger and shows more variation with angle than that for π⁻ production, and that b) the angular distribution and absolute cross section is very noticeably dependent on which final nuclear state is reached in the reaction.