Search for exclusive photoproduction of Z$_c^{\pm}$(3900) at COMPASS
  A search for the exclusive production of the $Z_c^{\pm}(3900)$ hadron by virtual photons has been performed in the channel $Z_c^{\pm}(3900)\rightarrow J/\psi \pi^{\pm}$. The data cover the range from 7 GeV to 19 GeV in the centre-of-mass energy of the photon-nucleon system. The full set of the 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%. 
C. Adolph, R. Akhunzyanov, M.G. Alexeev, G.D. Alexeev, A. Amoroso, V.   Andrieux, V. Anosov, A. Austregesilo, B. Badelek, F....
hep-ex