Measurement of the inclusive B_s^0 -> X^+ l^- \nu semileptonic decay branching fraction

Abstract

Inclusive semileptonic B_s^0 -> X^+ l^- \nu decays are studied for the first time using a 23.6 fb^{-1} data sample collected on the Y(5S) resonance with the Belle detector at the KEKB asymmetric energy e^+ e^- collider. These decays are identified by the means of a lepton accompanied by a same-sign D_s^+ meson originating from the other B_s^0 in the event. The semileptonic branching fractions are measured in the electron and muon channels to be Bf(B_s^0 -> X^+ e^- \nu) = (10.9 \pm 1.0 \pm 0.9)% and Bf(B_s^0 -> X^+ \mu^- \nu) = (9.2 \pm 1.0 \pm 0.8)%, respectively. Assuming an equal electron and muon production rate in B_s^0 decays, a combined fit yields an average leptonic branching fraction Bf(B_s^0 -> X^+ l^- \nu) = (10.2 \pm 0.8 \pm 0.9)%.