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

Abstract

We have searched for exclusive production of exotic charmonia in the reaction $\hat{I}{¼}^{+}N\to \hat{I}{¼}^{+}(J/\ddot{I}ˆ\ddot{I}{€}^{+}\ddot{I}{€}^{-})\ddot{I}{€}^{\pm }{N}^{\prime }$ using COMPASS data collected with incoming muons of 160 GeV/$c$ and 200 GeV/$c$ momentum. In the $J/\ddot{I}ˆ\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ mass distribution we observe a signal with a statistical significance of 4.1 $\ddot{I}ƒ$. Its mass and width are consistent with those of the $X(3872)$. The shape of the $\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ mass distribution from the observed decay into $J/\ddot{I}ˆ\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ shows disagreement with previous observations for $X(3872)$. The observed signal may be interpreted as a possible evidence of a new charmonium state. It could be associated with a neutral partner of $X(3872)$ with $C=-1$ predicted by a tetraquark model. The product of cross section and branching fraction of the decay of the observed state into $J/\ddot{I}ˆ\ddot{I}{€}^{+}\ddot{I}{€}^{-}$ is determined to be 71$\pm$28(stat)$\pm$39(syst) pb.

12 pages, 6 figures