Investigation of the Lightest Hybrid Meson Candidate with a Coupled-Channel Analysis of $bar{p}p$-, $pi^- p$- and $pipi$-Data

Based on new insights from two recent coupled-channel analyses of $bar{p}p$ annihilation together with $pipi$-scattering data and of $pi^- p$ data, this paper aims at a better understanding of the spin-exotic $pi_1$ resonances in the light meson sector. The Crystal Barrel Collaboration observed the $pi_1$-wave in $bar{p}p$ annihilations in flight for the first time with the coupling to $pi^0eta$ in the reaction $bar{p}p,rightarrow,pi^0pi^0eta$ with a sophisticated coupled-channel approach. Another refined coupled-channel analysis of the P- and D-waves in the $pieta$ and $pieta^prime$ system based on data measured at COMPASS has been performed by the JPAC group. In that study the two spin-exotic signatures listed in the PDG, the $pi_1(1400)$ and $pi_1(1600)$, with a separate coupling to $pieta$ and $pieta^prime$ can be described by a single pole. In this paper, both analyses, the one with the three $bar{p}p$ annihilation channels into $pi^0pi^0eta$, $pi^0etaeta$ and $K^+K^-pi^0$ and 11 different $pipi$-scattering data sets and the one with the P- and D-wave data in the $pieta$ and $pieta^prime$ systems measured at COMPASS, are subjected to a combined coupled channel analysis. By utilizing the K-matrix approach and realizing the analyticity via Chew-Mandelstam functions the $pi_1$ wave can be well described by a single pole for both systems, $pieta$ and $pieta^prime$. The mass and width of the $pi_1$-pole are measured to be $(1561.6 , pm , 3.0 , ^{+6.6}_{-2.6},), mathrm{MeV/c}^2$ and $(388.1 , pm , 5.4 , ^{+0.2}_{-14.1},), mathrm{MeV}$.