Étude de la diffusion π-He entre 500 et 1200 MeV

Abstract

A counter experiment has been made to study the π-He interaction, in the (500÷1200) MeV energy range. Measurements of the integral distribution of charged secondaries for forward angles between 4° and 30° in the laboratory system have been performed. The interpretation has been made in the frame of the optical model, but the results have led to a careful re-examination of the usual approximations of this model. While the validity of the impulse approximation is confirmed, it has been found that both the nonlocality of nucleon forces and the Fermi motion of nucleons have to be reconsidered. The nonlocality of nuclear forces leads to an apparent difference between «electromagnetic» and «nuclear» radii of the nucleus. The difference has been estimated. The Fermi motion of the nucleons gives a displaying of the π-nucleon interaction energies, and, consequently, to a smoothing of the mean π-bound nucleon total cross-section\(\bar \sigma \) (which is related to the optical potential) in the πN resonances region. Using thea) andb) considerations, a good agreement has been got between the experimental results and the theoretical predictions issued from the known π-nucleon interaction. Some estimates concerning the elastic differential π-He cross-sections in the above framework are shown in the last Section.