First Observation of the Decay B s 0 → K − μ + ν μ and a Measurement of | V u b | / | V c b |

Abstract

© 2021 CERN. The first observation of the suppressed semileptonic Bs0→K-μ+νμ decay is reported. Using a data sample recorded in pp collisions in 2012 with the LHCb detector, corresponding to an integrated luminosity of 2 fb-1, the branching fraction B(Bs0→K-μ+νμ) is measured to be [1.06±0.05(stat)±0.08(syst)]×10-4, where the first uncertainty is statistical and the second one represents the combined systematic uncertainties. The decay Bs0→Ds-μ+νμ, where Ds- is reconstructed in the final state K+K-π-, is used as a normalization channel to minimize the experimental systematic uncertainty. Theoretical calculations on the form factors of the Bs0→K- and Bs0→Ds- transitions are employed to determine the ratio of the Cabibbo-Kobayashi-Maskawa matrix elements |Vub|/|Vcb| at low and high Bs0→K- momentum transfer.