Search for the lepton-flavour violating decays B0( s) → e±μ∓

Abstract A search for the lepton-flavour violating decays B s 0 → e ± μ ∓ and B 0 → e ± μ ∓ is performed based on a sample of proton-proton collision data corresponding to an integrated luminosity of 3 fb−1, collected with the LHCb experiment at centre-of-mass energies of 7 and 8 TeV. The observed yields are consistent with the background-only hypothesis. Upper limits on the branching fraction of the B s 0 → e ± μ ∓ decays are evaluated both in the hypotheses of an amplitude completely dominated by the heavy eigenstate and by the light eigenstate. The results are $$ \frac{@}{@}\mathrm{\mathcal{B}}\left({B}_s^0\to {e}^{\pm }{\mu}^{\mp}\right)<6.3(5.4)\times 1{0}^{-9} $$ @ @ ℬ B s 0 → e ± μ ∓ < 6.3 5.4 × 1 0 − 9 and $$ \frac{@}{@}\mathrm{\mathcal{B}}\left({B}_s^0\to {e}^{\pm }{\mu}^{\mp}\right)<7.2(6.0)\times 1{0}^{-9} $$ @ @ ℬ B s 0 → e ± μ ∓ < 7.2 6.0 × 1 0 − 9 at 95% (90%) confidence level, respectively. The upper limit on the branching fraction of the B 0 → e ± μ ∓ decay is also evaluated, obtaining $$ \frac{@}{@}\mathrm{\mathcal{B}}\left({B}^0\to {e}^{\pm }{\mu}^{\mp}\right)<1.3(1.0)\times 1{0}^{-9} $$ @ @ ℬ B 0 → e ± μ ∓ < 1.3 1.0 × 1 0 − 9 at 95% (90%) confidence level. These are the strongest limits on these decays to date.