We report the first observation of a baryonic $B_s^0$ decay, $B_s^0 \to p \kern 0.1em\overline{ \kern -0.1em\Lambda} K^-$, using proton-proton collision data recorded by the LHCb experiment at center-of-mass energies of 7 and 8 TeV, corresponding to an integrated luminosity of $3.0\,\mathrm{ fb}^{ -1}$. The branching fraction is measured to be $ \mathcal{ B}(B_s^0 \to p \kern 0.1em\overline{ \kern -0.1em\Lambda} K^-) + \mathcal{ B}(B_s^0 \to \bar{ p} \Lambda K^+) = \left[5.46 \pm 0.61 \pm 0.57 \pm 0.50 (\mathcal{ B}) \pm 0.32 (f_s/f_d)\right]\times 10^{ -6}, $ where the first uncertainty is statistical and the second systematic, the third uncertainty accounts for the experimental uncertainty on the branching fraction of the $B^0 \to p \kern 0.1em\overline{ \kern -0.1em\Lambda} \pi^-$ decay used for normalization, and the fourth uncertainty relates to the knowledge of the ratio of $b$-quark hadronization probabilities $f_s/f_d$.
Categories: hep-ex