Interactions of high energy mesons with complex nuclei

Abstract

In order to study further the reaction of 300 MeV π (^-) mesons with carbon nuclei, it was necessary to acquire with good statistics the energy of the secondaries at different angular intervals. Apparatus was designed and built to support nuclear emulsion plates in a vertical plane around a central target. The apparatus was inserted between the poles of a magnet in a field of 25.5 kilogauss during the exposure. The plates were then area scanned for suitable tracks. A method of analysis was developed especially to cope with the problem of a finite target. pβ measurements were also made on secondaries from interactions in a carbon target. The actual incident beam energy was determined and was 285 MeV in both cases. The two sets of results agreed well over the angular interval where comparison could be made. The results were also compatible with previous experimental results at 300 MeV. Comparison was also made with the results predicted by a Monte Carlo nuclear cascade calculation (Bertini), but although the energy-angular distributions were almost identical, the momentum distributions at any one specific emission angle did not give good agreement. The observed angular distribution can be explained if the pion is subject to a potential on entering the nucleus, and if the nucleons have a momentum distribution extending up to at least 275 MeV/c. The nuclear well depth is estimated to be on average 53 MeV. An exclusion principle operates preventing pion-nucleon interaction if the nucleon is not thereby raised to the top of the nuclear well.