Speaker
Description
A search for the rare decay $B^+\to\bar{\Lambda} p\mu^+\mu^-$ is performed using proton-proton collision data recorded by the LHCb experiment at a centre-of-mass energy of $\sqrt{s}= 13$ TeV, corresponding to an integrated luminosity of 5.4 fb$^{-1}$. An excess of events is found with respect to the background-only expectation, with a signal significance of 3.5 standard deviations, in the threshold-mass-enhanced region of $m(\bar{\Lambda} p)<2.8 \rm{Gev/c^2}$. The branching fraction is measured to be ${\cal B}(B^+\to\bar{\Lambda} p\mu^+\mu^-)|_{m(\bar{\Lambda} p)<2.8 \rm{Gev/c^2}}=(1.70 \pm 0.60_{\rm stat} \pm 0.19_{\rm syst} \pm 0.14_{\rm ext}) \times 10^{-8}$, where the last uncertainty is due to external inputs on ${\cal B}(B^+ \to \bar{\Lambda} p J/\psi)\times {\cal B}(J/\psi \to \mu^+\mu^-)$. With no obvious signal observed in the high \lamp region, an upper limit is set to be ${\cal B}(B^+\to\bar{\Lambda} p\mu^+\mu^-)|_{m(\bar{\Lambda} p)>2.8~\text{GeV}/c^2}<2.4 \times 10^{-9}$ at 90\% confidence level.
