Antiproton-proton annihilations into five pions at 5.7 GeV/c

Abstract

A study of 872 events of the reaction\(\bar pp \to \pi ^ + \pi ^ + \pi ^ - \pi ^ - \pi ^0 \) is reported. The cross-section for this reaction is found to be (0.9±0.1) mb. The positive pions tend to be emitted in the direction of the proton and the negative pions in the direction of the antiproton. The forward to backward and polar to equatorial ratios(F−B/(F+B) and(P−E)/(P+E) are found to be 0.17±0.02 and 0.27±0.02 respectively, the former value corresponding to an excess of two-thirds of a π+ or a π− per event in the backward or forward direction respectively in the c.m.s. There is a considerable amount of\(\rho ^{0^ \pm } \) and f0 resonance production but no A1, A2 or B meson production has been observed. No evidence for an associated production of resonances has been found which makes any simple interpretation of the annihilation process in terms of three-meson final states diffcult. In the π+π−π0 mass distribution an enhancement is seen with a mass (2207±13) MeV and width (62±52) MeV which could correspond to the neutrally charged state of the peak observed by Chikovaniet al. at 2195 MeV. A simple model is proposed which explains part of the data on four- and five-pion annihilations. *** DIRECT SUPPORT *** A09E0041 00009