Observation of the ${\Xi }_b^{-}\to {\Xi }^{-}{\mu }^{+}{\mu }^{-}$ and study of the ${\Xi }_b^{-}\to {\Xi }^{-}\psi (2S)$ decays

Abstract

The rare decay ${\Xi }_b^{-}\to {\Xi }^{-}{\mu }^{+}{\mu }^{-}$ is observed for the first time using proton-proton collision data collected by the LHCb experiment at centre-of-mass energies of $7$, $8$ and~$13\text{TeV}$, corresponding to integrated luminosities of $1$, $2$ and $6{\text{fb}}^{-1}$, respectively. Its branching fraction is reported in intervals of the dimuon invariant mass squared. The integrated value of $\mathcal{B}({\Xi }_b^{-}\to {\Xi }^{-}{\mu }^{+}{\mu }^{-})$ is measured to be $(118\pm 24\pm 7\pm 38)\times 10^{-8}$, where the first uncertainty is statistical, the second is systematic and the third uncertainty arises from the normalisation branching fraction $\mathcal{B}({\Xi }_b^{-}\to {\Xi }^{-}J/\psi )$, whose uncertainty is dominated by SU(3)-breaking effects. In addition, the ratio of the branching fractions of the ${\Xi }_b^{-}\to {\Xi }^{-}\psi (2S)$ and the ${\Xi }_b^{-}\to {\Xi }^{-}J/\psi$ decays is measured to be $0.491\pm 0.041\pm 0.019$.

arXiv commentAll figures and tables, along with any supplementary material and additional information, are available at https://lhcb-glance.cern.ch/alcm/public/analysis/full-details/6426/