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We have searched for exclusive production of exotic charmonia in the reaction$\mu^+~N \rightarrow \mu^+ (J\!/\!\psi\pi^+\pi^-)\pi^{\pm}~N'$ using COMPASSdata collected with incoming muons of 160 GeV/$c$ and 200 GeV/$c$ momentum. Inthe $J\!/\!\psi\pi^+\pi^-$ mass distribution we observe a signal with astatistical significance of 4.1 $\sigma$. Its mass and width are consistentwith those of the $X(3872)$. The shape of the $\pi^+\pi^-$ mass distributionfrom the observed decay into $J\!/\!\psi\pi^+\pi^-$ shows disagreement withprevious observations for $X(3872)$. The observed signal may be interpreted asa possible evidence of a new charmonium state. It could be associated with aneutral partner of $X(3872)$ with $C = -1$ predicted by a tetraquark model. Theproduct of cross section and branching fraction of the decay of the observedstate into $J\!/\!\psi\pi^+\pi^-$ is determined to be71$\pm$28(stat)$\pm$39(syst) pb.

Search for muoproduction of $X(3872)$ at COMPASS and indication of a new state $\widetilde{X}(3872)$