Observation of the decay $\Xi_b^- \to pK^-K^-$

Abstract

Decays of the $\Xi^-_b$ and $\Omega^-_b$ baryons to the charmless final states $ph^-h^{\prime -}$, where $h^{(\prime)}$ denotes a kaon or pion, are searched for with the LHCb detector. The analysis is based on a sample of proton-proton collision data collected at center-of-mass energies $\sqrt{s}$ = 7 and 8 TeV, corresponding to an integrated luminosity of 3  fb$^{−1}$. The decay $\Xi_b^- \to pK^-K^-$ is observed with a significance of 8.7 standard deviations, and evidence at the level of 3.4 standard deviations is found for the $\Xi_b^- \to pK^-\pi^-$ decay. Results are reported, relative to the $B^- \to K^+K^-K^-$ normalization channel, for the products of branching fractions and b-hadron production fractions. The branching fractions of $\Xi_b^- \to pK^-\pi^-$ and $\Xi_b^- \to p\pi^-\pi^-$ relative to $\Xi_b^- \to pK^-K^-$ decays are also measured.