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


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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 $3.7times10^{-3}$ has been established at the confidence level of 90%.

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