Non-strange light-meson spectroscopy at COMPASS

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 $1.65\mathrm{G}\mathrm{e}\mathrm{V}\mathrm{/}{c}^2$ in $b_1(1235)\pi$ partial waves is consistent with the expected ${\pi }_1(1600)$.