Meson production from diffractive pion dissociation at COMPASS

Diffractive dissociation reactions at COMPASS provide clean access to mesons with masses below $\approx$ 2.5GeV$/c^{2}$. This paper presents a partial wave analysis of about 420 000 $\pi^{-}Pb\rightarrow\pi^{-}\pi^{-}\pi^{+}Pb$ events at 190 GeV$/c$ beam momentum and with four-momentum transfer $t'\in$ [0.1, 1] GeV$^{2}/c^{2}$. The well-known $a_{1}$(1260), $a_{2}$(1320) and $\pi_{2}$(1670) mesons are resolved with high quality. Also the less established states $\pi$(1800) and $a_{4}$(2040) are seen. In addition, a resonance in the spin-exotic $J^{PC} =$ 1$^{−+}$ wave is observed. A mass-dependent fit results in a mass and width of 1.660$^{+0.010}_{−0.074}$ and 0.269$^{+0.063}_{−0.085}$ GeV$/c^{2}$, respectively, which is consistent with the disputed hybrid candidate $\pi_{1}$(1600).