Analysis of the diffractively produced $\pi^- \pi^- \pi^+$ final state at COMPASS

The COMPASS experiment at CERN collected a large sample of diffractively produced $π ^−π^ −π^ +$ events. The data contain contributions from light-meson resonances with the quantum numbers of πJ - and aJ -like states. We performed a partial-wave analysis of this final state for proton and nuclear targets. We consistently observe a π-like signal with $J^{PC} = 0^{−+}$ in the $f_2(1270)πD$ wave. The signal appears to be incompatible with the established π(1800) resonance, which we observe in the decays into $(ππ)SπS, f_0(980)πS$ and $f_0(1500)πS$ waves.