Measurement of B(B$_{s}$ →d$_{s}$X) with B$_{s}$ semileptonic tagging

We report the first direct measurement of the inclusive branching fraction B(B$_{s}$ →D$_{s}$X) via B$_{s}$ tagging in e$^{+}$e$^{–}$→Υ(5S) events. Tagging is accomplished through a partial reconstruction of semileptonic decays B$_{s}$→D$_{s}$Xℓν, where X denotes unreconstructed additional hadrons or photons and ℓ is an electron or muon. With 121.4 fb$^{–1}$ of data collected at the Υ(5S) resonance by the Belle detector at the KEKB asymmetric-energy e$^{+}$e$^{–}$ collider, we obtain B(B$_{s}$ →D$_{s}$X)=(60.2±5.8±2.3)%, where the first uncertainty is statistical and the second is systematic.