On the disputed $\pi_1(1600)$ resonance and observation of a new iso-vector resonance

Abstract

The COMPASS experiment at CERN delivers new results on the search for exotic mesons. A spin-exotic resonance, the $\pi_1(1600)$, was reported by several experiments in the past. Those observations are, however, still to date highly disputed in the community. Especially the $\rho\pi$ decay channel allows for simultaneous observation of well established and less known resonances in different decay modes. The results from amplitude analysis of diffractively produced $(3\pi)^{-}$ final states show consistently a spin-exotic signal, that appears in agreement with previous observations of the $\pi_1(1600)$. The high-statistics 2008 data sample allows and demands for an extended amplitude analysis method that further disentangles resonant and non-resonant particle production. The present status of analysis of COMPASS data and the observation of a new iso-vector meson $a_1(1420)$ is discussed.