Measurement of B ( B s → D s X ) with B s semileptonic tagging

Abstract

e report the first direct measurement of the inclusive branching fraction B ( B s → D s X ) via B s tagging in e + e − → Υ ( 5 S ) events. Tagging is accomplished through a partial reconstruction of semileptonic decays B s → D s X ℓ ν , 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 ( 5 S ) 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