Lattice-QCD predicts the exotic meson $\pi_1(1600)$ to dominantly decay to $b_1\pi$. The $b_1\pi$ decay channel is accessible via the $\omega\pi^{ -}\pi^{ 0}$ final state. COMPASS recorded the so far largest data set of this final state. A partial-wave analysis allows to determine the resonant content in this final state including possible contributions from $\pi_1(1600)$. Decomposing the measured intensity into amplitudes of partial waves gives a first qualitative insight into contributing intermediate states. We observe signals in agreement with well-established states like the $\pi(1800)$ and $a_4(1970)$. Smaller resonance-like signals are visible in the $J^{ PC}$ sectors $3^{ ++}$ and $6^{ ++}$, where possible states were claimed but none are established. For $J^{ PC}=1^{ -+}$ a signal at $1.65\,\mathrm{ GeV/}c^{ 2}$ in $b_1(1235)\pi$ partial waves is consistent with the expected $\pi_1(1600)$.
Categories: hep-ex