Spin-exotic search in the $\rho\pi$ decay channel: New results on $\pi^{-}\pi^{0}\pi^{0}$ in comparison to $\pi^{-}\pi^{+}\pi^{-}$ final states (diffractively produced on proton)

Abstract

The COMPASS experiment at CERN SPS features charged particle tracking as well as good coverage by electromagnetic calorimetry, and our data provide an excellent opportunity for simultaneous observation of new states in different decay modes by the same experiment. The existence of the spin-exotic $\pi_1(1600)$ resonance in the $\rho\pi$ decay channel is studied for the first time at COMPASS in both decay modes of the diffractively produced $(3\pi)^{-}$ system: $\pi^{-}p \rightarrow \pi^{-}\pi^{+}\pi^{-}p$ and $\pi^{-} p \rightarrow \pi^{-}\pi^{0}\pi^{0} p$. A preliminary partial-wave analysis performed on the 2008 proton target data allows for a first conclusive comparison of both $(3\pi)^{-}$ decay modes not only for main waves but also for small ones. We find the neutral versus charged mode results in excellent agreement with expectations from isospin symmetry. Both, the intensities and the relative phases to well-known resonances, are consistent for the neutral and the charged decay modes of the $(3\pi)^{-}$ system. The status on the search for the spin-exotic $\pi_1(1600)$ resonance produced on a proton target is discussed.