Search for exclusive photoproduction of $Z_c(3900)$ at COMPASS

Abstract

The $Z_{c}(3900)$ hadron state has been found by the BES-III and Belle experiments in the decay of the hadron state with higher mass. The first attempt to search for the direct exclusive production of the $Z_c^{\pm}(3900)$ hadron by virtual photons has been performed in the reaction $\mu^+ N \rightarrow \mu^+ N' Z_c(3900)^{\pm} \rightarrow \mu^+ N' J/\psi \pi^{\pm}$ at COMPASS \cite{Adolph:2014hba}. The data cover the range from 7~GeV to 19~GeV in the centre-of-mass energy of the photon-nucleon system. The full COMPASS data set collected with a muon beam between 2002 and 2011 has been used. An upper limit for the ratio $BR(Z_c^{\pm}(3900)\rightarrow J/\psi \pi^{\pm} )\times (\sigma_{ \gamma~N \rightarrow Z_c^{\pm}(3900)~ N} /\sigma_{ \gamma~N \rightarrow J/\psi~ N})$ of $3.7\times10^{-3}$ has been established at the confidence level of 90\%.