Speaker
Alexey Guskov
(Joint Inst. for Nuclear Research (RU))
Description
The $Z_{c}(3900)$ hadron state has been found by the BES-III experiment in the decay
of a 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 channel $Z_c^{\pm}(3900)\rightarrow J/\psi \pi^{\pm}$ at COMPASS.
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%.
Author
Alexey Guskov
(Joint Inst. for Nuclear Research (RU))
