Search for the lepton-flavour violating decays $B_s^0\to e^{\pm }\hat{I}{¼}^{\mp }$ and $B^0\to e^{\pm }\hat{I}{¼}^{\mp }$

Abstract

A search for the lepton-flavour violating decays $B_s^0\to e^{\pm }\hat{I}{¼}^{\mp }$ and $B^0\to e^{\pm }\hat{I}{¼}^{\mp }$ is performed with a data sample, corresponding to an integrated luminosity of 1.0 fb${}^{-1}$ of $pp$ collisions at $\sqrt{s}=7$ TeV, collected by the LHCb experiment. The observed number of $B_s^0\to e^{\pm }\hat{I}{¼}^{\mp }$ and $B^0\to e^{\pm }\hat{I}{¼}^{\mp }$ candidates is consistent with background expectations. Upper limits on the branching fractions of both decays are determined to be $BR(B_s^0\to e^{\pm }\hat{I}{¼}^{\mp })<1.1(1.4)\times 10^{-8}$ and $BR(B^0\to e^{\pm }\hat{I}{¼}^{\mp })<2.8(3.7)\times 10^{-9}$ at 90% (95%) confidence level (C.L.). These limits are a factor of twenty lower than those set by previous experiments. Lower bounds on the Pati-Salam leptoquark masses are also calculated, $M_{\mathrm{LQ}}(B_s^0\to e^{\pm }\hat{I}{¼}^{\mp })>107$ TeV/c${}^2$ and $M_{\mathrm{LQ}}(B^0\to e^{\pm }\hat{I}{¼}^{\mp })>126$ TeV/c${}^2$ at 95% C.L., and are a factor of two higher than the previous bounds.

version published on Phys. Rev. Lett. (7 pages, 2 figures)