New analysis of $\eta\pi$ tensor resonances measured at the COMPASS experiment

TL;DR

This paper presents a new amplitude analysis of $ ext{ηπ}$ tensor resonances from COMPASS data, identifying and characterizing the $a_2(1320)$ and $a_2^ ext{'}(1700)$ resonances with detailed pole position measurements.

Contribution

It introduces an analytical model based on the relativistic S-matrix principles to analyze tensor resonances in $ ext{ηπ}$ scattering, providing precise resonance parameters.

Findings

Identification of $a_2(1320)$ and $a_2^ ext{'}(1700)$ resonances.

Precise measurements of their masses and widths.

Comprehensive pole position analysis.

Abstract

We present a new amplitude analysis of the $\eta\pi$ $D$-wave in $\pi^- p\to \eta\pi^- p$ 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 $a_2(1320)$ and the excited $a_2^\prime(1700)$, and perform a comprehensive analysis of their pole positions. For the mass and width of the $a_2$ we find $M=(1307 \pm 1 \pm 6)$~MeV and $\Gamma=(112 \pm 1 \pm 8)$~MeV, and for the excited state $a_2^\prime$ we obtain $M=(1720 \pm 10 \pm 60)$~MeV and $\Gamma=(280\pm 10 \pm 70)$~MeV, respectively.