Measurement of the B[subscript s]⁰→μ⁺μ⁻ Branching Fraction and Effective Lifetime and Search for B⁰→μ⁺μ⁻ Decays

Abstract

Further distribution of this work must maintain attribution to the author(s) and the published article's title, journal citation, and DOI. A search for the rare decays B[subscript s]⁰→μ⁺μ⁻ and B⁰→μ⁺μ⁻ is performed at the LHCb experiment using data collected in pp collisions corresponding to a total integrated luminosity of 4.4 fb⁻¹. An excess of B[subscript s]⁰→μ⁺μ⁻ decays is observed with a significance of 7.8 standard deviations, representing the first observation of this decay in a single experiment. The branching fraction is measured to be B(B[subscript s]⁰→μ⁺μ⁻ )=(3.0±0.6-0.2+0.3)×10⁻ ⁹, where the first uncertainty is statistical and the second systematic. The first measurement of the B⁰→μ⁺μ⁻ effective lifetime, τ(B[subscript s]⁰→μ⁺μ⁻)=2.04±0.44±0.05 ps, is reported. No significant excess of B⁰→μ⁺μ⁻ decays is found, and a 95% confidence level upper limit, B(B⁰→μ⁺μ⁻)<3.4×10-10, is determined. All results are in agreement with the standard model expectations.