Partial-wave decomposition of the diffractively produced $\pi^-\pi^+\pi^-\eta$ final state at COMPASS

One of the prime goals of the COMPASS experiment at CERN is the study of the light meson spectrum, with a particular emphasis on the search for exotic states. We present the first high-statistics partial-wave decomposition of the diffractive reaction $\pi^-+p\to \pi^-\pi^+\pi^-\eta+p$, which spans a wide range of decay channels, such as $f_1(1285)\pi^-$, $a_2^-(1320)\eta$, $\eta^\prime\pi^-$, and $\rho(770)a_0^-(980)$. This analysis also includes decay channels, i.e. $f_1(1285)\pi^-$ and $\eta^\prime\pi^-$, predicted by theoretical models for the lightest hybrid meson and providing the opportunity to verify the hybrid meson hypothesis of the $\pi_1(1600)$.