Search for the lepton-flavour violating decays $B^0_{(s)} \rightarrow e^\pm \mu^\mp$

TL;DR

This paper reports a search for lepton-flavour violating decays of B mesons using LHCb data, setting the most stringent upper limits to date on their branching fractions, with no evidence of such decays observed.

Contribution

It provides the first and most restrictive upper limits on $B^0_{(s)} ightarrow e^\pm \mu^\mp$ decays based on 3 fb$^{-1}$ of LHCb data, improving previous constraints.

Findings

No significant excess observed over background.

Upper limits on branching fractions are set at $5.4 imes 10^{-9}$ for $B_s^0$ and $1.0 imes 10^{-9}$ for $B^0$.

These are the strongest limits to date on these lepton-flavour violating decays.

Abstract

A search for the lepton-flavour violating decays $B^0_s \rightarrow e^\pm \mu^\mp$ and $B^0 \rightarrow e^\pm \mu^\mp$ 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 fractions are determined to be $\mathcal{B}(B^0_s \rightarrow e^\pm \mu^\mp) < 5.4\,(6.3) \times 10^{-9}$ and $\mathcal{B}(B^0 \rightarrow e^\pm \mu^\mp) < 1.0\,(1.3) \times 10^{-9}$ at $90\%\,(95\%)$ confidence level, which are the strongest limits on these decays to date.