The Exotic $eta_s14pi^-$ Wave in 190 GeV $pi^-p -> pi^-eta_s14p$ at COMPASS

Abstract

A sample of 35,000 events of the type pi-p --> eta_s14pi-p_slow (eta_s14 --> eta pi-pi_s16, eta --> gamma gamma) with -t>0.1 GeV^2/c^2 was selected from COMPASS 2008 data for a partial-wave analysis. We study the broad P__s16 structure known from previous experiments at lower energies, in particular its phase motion relative to the D__s16-wave near the a_2(1320) mass and relative to a broad D__s16-wave structure at higher mass. We also find the a_4(2040). We compare kinematic plots for the eta_s14pi^- and eta pi- final states.