  Exotic charmonium-like states have been observed by various experiments over
the last 15 years, but their nature is still under discussion.
Photo-(muo)production is a new promising instrument to study them. COMPASS, a
fixed target experiment at CERN, analyzed the full set of the data collected
with a muon beam between 2002 and 2011, covering the range from 7 GeV to 19 GeV
in the centre-of-mass energy of the virtual photon-nucleon system. A signal in
the mass spectrum of $J/\psi\pi^+\pi^-$ with the statistical significance of
4.1 $\sigma$ was observed in the reaction $\mu^+~N \rightarrow
\mu^+(J/\psi\pi^+\pi^- )\pi^{\pm} N'$. Its mass and width are consistent with
those of the $X(3872)$. The shape of the $\pi^+\pi^-$ mass distribution from
the observed decay into $J/\psi\pi^+\pi^-$ is different from previous
observations for $X(3872)$. The observed signal may be interpreted as possible
evidence of a new charmonium state $\widetilde{X}(3872)$. It could be
associated with a neutral partner of $X(3872)$ with $C = -1$ predicted by a
tetraquark model.
