Measurement of the Bs0 → μ+μ- Branching Fraction and Search for B0 → μ+μ- Decays at the LHCb Experiment

A search for the rare decays B-s(0) -> mu(+)mu(-) and B-0 -> mu(+)mu(-) is performed at the LHCb experiment. The data analyzed correspond to an integrated luminosity of 1 fb(-1) of pp collisions at a center-of-mass energy of 7 TeV and 2 fb(-1) at 8 TeV. An excess of B-s(0) -> mu(+)mu(-) signal candidates with respect to the background expectation is seen with a significance of 4.0 standard deviations. A time-integrated branching fraction of B(B-s(0) -> mu(+)mu(-)) = (2.9(-1.0)(+1.1)) x 10(-9) is obtained and an upper limit of B(B-0 -> mu(+)mu(-)) < 7.4 x 10(-10) at 95% confidence level is set. These results are consistent with the standard model expectations.