Observation of the decay $\chi_{c1}(3872)\rightarrow J\mskip -3mu/\mskip -2mu\psi \mu^+\mu^-$

Abstract

The first observation of the $\chi_{c1}(3872)\rightarrow J\mskip -3mu/\mskip -2mu\psi \mu^+\mu^-$ decay is reported using proton-proton collision data recorded with the LHCb detector corresponding to an integrated luminosity of $9fb^{-1}$. The decay mode is observed for the first time, with a significance of $6.5\sigma$. Its branching fraction is measured relative to the $\chi_{c1}(3872)\rightarrow J\mskip -3mu/\mskip -2mu\psi \pi^+\pi^-$ decay mode \begin{align*} \frac{\cal{BF}(\chi_{c1}(3872)\rightarrow J\mskip -3mu/\mskip -2mu\psi \mu^+\mu^-)}{\cal{BF}(\chi_{c1}(3872)\rightarrow J\mskip -3mu/\mskip -2mu\psi \pi^+\pi^-)} = \left(1.68\pm 0.32\pm 0.05\right)\times10^{-3}, \end{align*} where the first uncertainty includes both statistical contributions and systematic contributions which are uncorrelated between data-taking periods, and the second represents the systematic contributions that are correlated between data-taking periods.