Resonances of the systems pi-eta and pi-eta_s14 in the reactions pi-p --> pi-eta p and pi-p --> pi-eta_s14 p at COMPASS

Abstract

We describe partial-wave analyses of the systems pi-eta and pi-eta_s14 produced in interactions of a pi- beam (190 GeV/c) with a liquid hydrogen target. The data were recorded during the 2008 COMPASS run, where a slow recoiling proton (|t|>0.1 GeV^2) was required by the trigger. We compare analyses of the pi-eta and pi-eta_s14 data. Significant contributions can be attributed to the resonances a_2(1320), observed in the D__s16-wave, and a_4(2040), observed in the G__s16-wave. Between the two systems, we find similar compositions of the even partial waves D__s16 and G__s16 after taking phase-space factors into account, but a much enhanced P__s16-wave in pi-eta_s14. Relative phase-differences indicate a large incoherent contribution of in the P__s16-wave of the eta_s14pi- system, but other interpretations are not excluded. The known resonances a_2(1320), a_4(2040) and their parameters could be extracted from the data/ their branchings are found to roughly agree with predictions from etaeta_s14 mixing.