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

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 $a_2^{\mathrm{\prime }}(1700)$, 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 $\mathrm{\Gamma }=(112\pm 1\pm 8)$~MeV, and for the excited state $a_2^{\mathrm{\prime }}$ we obtain $M=(1720\pm 10\pm 60)$~MeV and $\mathrm{\Gamma }=(280\pm 10\pm 70)$~MeV, respectively.