Measurement of the inclusive B0 s→ X+ℓ-ν semileptonic decay branching fraction

Inclusive semileptonic B0 s → X+ℓ-ν decays are studied for the first time using a 23.6 fb-1 data sample collected on the (5S) resonance with the Belle detector at the KEKB asym-metric energy e +e- collider. These decays are identified by the means of a lepton accompa- nied by a same-sign D+s meson originating from the other B0 s in the event. The semileptonic branching fractions are measured in the electron and muon channels to be B(B0 s → X+e -ν) =(10.9 ± 1.0 ± 0.9)% and B(B0 s → X+μ-ν) = (9.2 ± 1.0 ± 0.8)%, respectively. Assuming an equalelectron and muon production rate in B 0 s decays, a combined fit yields an average leptonic branch- ing fraction B(B0 s → X+ℓ-ν) = (10.2 ± 0.8 ± 0.9)%.