Partial-wave analyses of the (3π)-system in the reaction π−p → π−π−π+p at 11.2 GeV/ c

Abstract

The results are presented of two partial-wave analyses of the (3π) − system in 30 000 events of the reaction π −p → π − π − π +p at 11.2 GeV/ c. Both techniques incorporate the assumptions of the isobar model and are (a) the University of Illinois program which fits in terms of the (3π) density matrix elements and (b) an amplitude parametrisaton including possible effects of both spin non-flip and spin flip at the baryon vertex. The results obtained with these independent programs are found to be very close. The proportions of contributing states, their t-dependence and the phases of off-diagonal density matrix elements are discussed for the mass range 0.9 M(3 π) 1.9 GeV/ c 2. The A 1 phenomenon is investigated in the context of a recent model; values of the mass, width and cross sections for the A 1, A 2, A 3 states are given, and an interesting variation in the 2 +P M=1 wave is observed at high masses.