Angular Distribution of Charge Exchange and Inelastic Neutrons inπ−−pInteractions at 313 and 371 MeV

Abstract

Neutron angular distributions from the charge-exchange (71%) and inelastic modes (7r 0 ir°n, Tr + ir~n) of the ir~~-p interaction have been investigated at 313 and 371 MeV incident-pion kinetic energy. The data were obtained with an electronic counter system. Elastic and inelastic neutrons were separated in the all-neutral final states by time of flight. At both energies the charge-exchange differential cross section at the forward neutron angles differs from that determined by Caris et al. from measurements of the 7r°-decay gamma distributions, but generally agrees with the phase-shift-analysis calculations of Roper. The distribution of inelastic neutrons from both modes shows a strong preference for low center-of-mass neutron energies. The distribution of these neutrons does not correspond to that expected from the 1 = 0, W-TT interaction (ABC effect) suggested to account for the anomaly in p-d collisions observed by Abashian et aL Finally, all available charge-exchange differential-cross-section data from this and other experiments were combined by a least-squares fit to a Legendre expansion of the form

Pion-Nucleon Scattering in theP11State

“…Since it is known that the s-wave 7T-N forces are very weak, whereas the s-wave w-ir forces are very strong, the natural two-body configuration to consider is aN; a represents the ww 7=7=0 configuration at a mass of about 400 MeV. As a matter of fact, Brown and Singer have proposed that there is in fact a true resonance (i.e., a pole of a scattering amplitude) .^ Although much evidence has been cited in its favor, [41][42][43][44][45] the effect is noticeably absent in certain experiments such as the recent one on K e ± decays. 46 The possibility that there is an important enhancement without an actual resonance is difficult to exclude, particularly in view of the theoretical suggestion of Chew 47 that the ww phase shift may be decreasing through |TT.…”