A study of the low-mass part of the (Kππ) system in the reaction K-p→K-pπ+π- at 8.25 GeV/c

Abstract

The low-mass (Kππ) system of the reaction K-p → K-pπ+π- at 8.25 GeV/c is studied. The cross-section of this reaction is (0.97± ±0.04) mb. The dependence of the cross-section on the proton-proton momentum transfer shows broadening of the diffraction peak with respect to increasing (Kππ) mass. The production of two-body and three-body resonances is discussed with respect to their occurrence in the four longitudinal-momentum phase space sectors of pl(π+)vs. pl(π-). This allows to separate the three-body low-mass systems (Kππ) and (pππ), which can be produced diffractively, from the other quasi-two-body processes whose production mechanism is meson exchange. In order to discuss what spin-parity contributions can be distinguished in the lowmass (Kππ) system, the D-moments of the angular distributions of the (Kππ) system with respect to variation of its effective mass and to variation of the possible analyser directions are carried out. The result is that, in addition to the dominant JP=1+ content, there is a clearly identifiable JP=0- contribution to the low-mass (Kππ) system. This contribution can be estimated to be 10% by an analysis of the density of events in the Dalitz plot, which gives also that the ρ production amplitude with respect to the K*(890) production amplitude decreases with increasing (Kππ) mass. This result is in agreement with an analysis of the reaction K+p→ K+pπ+π-. In the Appendix are given the properties of the D-moments and their predictability or suppression with respect to various spin-parity contributions. © 1974 Società Italiana di Fisica