Search for the baryon- and lepton-number violating decays $B^0\to p{\mu }^{-}$ and $B_s^0\to p{\mu }^{-}$

A search for the baryon- and lepton-number violating decays $B^0\to p{\mu }^{-}$ and $B_s^0\to p{\mu }^{-}$ is performed at the LHCb experiment using data collected in proton-proton collisions at $\sqrt{s}$ = 7, 8 and 13 TeV, corresponding to integrated luminosities of 1, 2 and 6 fb${}^{-1}$, respectively. No significant signal for $B^0\to p{\mu }^{-}$ and $B_s^0\to p{\mu }^{-}$ decays is found and the upper limits on the branching fractions are determined to be $\mathcal{B}(B^0\to p{\mu }^{-})<2.6(3.1)\times {10}^{-9}$ and $\mathcal{B}(B_s^0\to p{\mu }^{-})<12.1(14.0)\times {10}^{-9}$, respectively, at 90$\mathrm{\%}$ (95$\mathrm{\%}$) confidence level. These are the first limits on these decays to date.