New analysis of ηπ tensor resonances measured at the COMPASS experiment

A Jackura,C Fernández-Ramírez,M Mikhasenko,A Pilloni,V Mathieu,J Nys,V Pauk,A.P Szczepaniak,G Fox

doi:10.1016/j.physletb.2018.01.017

A Jackura, C Fernández-Ramírez + Show 7 more

Open Access

https://doi.org/10.1016/j.physletb.2018.01.017

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Abstract

We present a new amplitude analysis of the ηπ D-wave in the reaction π−p→ηπ−p measured by COMPASS. Employing an analytical model based on the principles of the relativistic S-matrix, we find two resonances that can be identified with the a2(1320) and the excited a2′(1700), and perform a comprehensive analysis of their pole positions. For the mass and width of the a2 we find M=(1307±1±6) MeV and Γ=(112±1±8) MeV, and for the excited state a2′ we obtain M=(1720±10±60) MeV and Γ=(280±10±70) MeV, respectively.

Highlights

The spectrum of hadrons contains a number of poorly determined or missing resonances, the better knowledge of which is of key importance for improving our understanding of Quantum Chromodynamics (QCD)
Active research programs in this direction are being pursued at various experimental facilities, including the COMPASS and LHCb experiments at CERN [1, 2, 3, 4], CLAS/CLAS12 and GlueX at JLab [5, 6, 7], BESIII at BEPCII [8], BaBar, and Belle [9]
Since we examine the partial wave intensities integrated over the momentum transfer t, we assume that the expansion coefficients are independent of t

Summary

Introduction

The spectrum of hadrons contains a number of poorly determined or missing resonances, the better knowledge of which is of key importance for improving our understanding of Quantum Chromodynamics (QCD). When resonances dominate the spectrum, which is the case studied here, unitarity is especially important since it constrains resonance widths and allows us to determine the location of resonance poles in the complex energy plane of the multivalued partial wave amplitudes. In 2014, COMPASS published high-statistics partial wave analyses of the π− p → η( )π− p reaction, at pbeam = 191 GeV [2]. The odd angular-momentum waves have exotic quantum numbers and exhibit structures that may be compatible with a hybrid meson [10]. The even waves show strong signals of non-exotic resonances. The D-wave exhibits a hint of the first radial excitation, the a2(1700) [11]

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