Light isovector resonances in π−p→π−π−π+p at 190 GeV/c

Abstract

We have performed the most comprehensive resonance-model fit of π−π−π+ states using the results of our previously published partial-wave analysis (PWA) of a large data set of diffractive-dissociation events from the reaction π−+p→π−π−π++precoil with a 190 GeV/c pion beam. The PWA results, which were obtained in 100 bins of three-pion mass, 0.5<m3π<2.5 GeV/c2, and simultaneously in 11 bins of the reduced four-momentum transfer squared, 0.1<t′<1.0 (GeV/c)2, are subjected to a resonance-model fit using Breit-Wigner amplitudes to simultaneously describe a subset of 14 selected waves using 11 isovector light-meson states with JPC=0−+, 1++, 2++, 2−+, 4++, and spin-exotic 1−+quantum numbers. The model contains the well-known resonances π(1800), a1(1260), a2(1320), π2(1670), π2(1880), and a4(2040). In addition, it includes the disputed π1(1600), the excited states a1(1640), a2(1700), and π2(2005), as well as the resonancelike a1(1420). We measure the resonance parameters mass and width of these objects by combining the information from the PWA results obtained in the 11 t′ bins. We extract the relative branching fractions of the ρ(770)π and f2(1270)πdecays of a2(1320) and a4(2040), where the former one is measured for the first time. In a novel approach, we extract the t′ dependence of the intensity of the resonances and of their phases. The t′dependence of the intensities of most resonances differs distinctly from the t′ dependence of the nonresonant components. For the first time, we determine the t′ dependence of the phases of the production amplitudes and confirm that the production mechanism of the Pomeron exchange is common to all resonances. We have performed extensive systematic studies on the model dependence and correlations of the measured physical parameters.