Study of the rare decay $J/\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}\hat{I}{¼}^{+}\hat{I}{¼}^{-}$

Abstract

The rare electromagnetic $J/\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}\hat{I}{¼}^{+}\hat{I}{¼}^{-}$ decay is observed with a significance greatly exceeding the discovery threshold, using proton-proton collision data collected by the LHCb experiment during 2016-2018 at a center-of-mass energy of 13 TeV, corresponding to an integrated luminosity of $5.4{\text{fb}}^{-1}$. The rate of this decay is measured relative to that of the $J/\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ mode. Using the QED model for the four-muon decay in the efficiency estimation, its branching fraction is determined to be \begin{equation*} {\mathcal{B}}(J/ψ\to μ^+μ^-μ^+μ^-) = (1.13\pm0.10\pm0.05\pm0.01)\times 10^{-6}, \end{equation*} where the uncertainties are statistical, systematic and due to the uncertainty on the branching fraction of the $J/\ddot{I}ˆ\to \hat{I}{¼}^{+}\hat{I}{¼}^{-}$ decay.

All figures and tables, along with machine-readable versions and any supplementary material and additional information, are available at https://lbfence.cern.ch/alcm/public/analysis/full-details/3453 (LHCb public pages)