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

TL;DR

This paper presents a detailed partial-wave analysis of ta and ta' systems produced in high-energy pion-proton interactions, identifying known resonances and comparing their properties with theoretical predictions.

Contribution

It provides the first comparative analysis of ta and ta' systems at COMPASS, revealing resonance contributions and phase behaviors, with implications for ta-ta' mixing models.

Findings

Identification of a_2(1320) and a_4(2040) resonances in the data.

Similar partial wave compositions in ta and ta' systems after phase-space correction.

Enhanced P_+-wave in ta' system indicating large incoherent contributions.

Abstract

We describe partial-wave analyses of the systems \pi-\eta and \pi-\eta' 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' data. Significant contributions can be attributed to the resonances a_2(1320), observed in the D_+-wave, and a_4(2040), observed in the G_+-wave. Between the two systems, we find similar compositions of the even partial waves D_+ and G_+ after taking phase-space factors into account, but a much enhanced P_+-wave in \pi-\eta'. Relative phase-differences indicate a large incoherent contribution of in the P_+-wave of the \eta'\pi- 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 \eta\eta' mixing.