First observation of Bs→Ds2∗+Xμν decays

Abstract

Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the semileptonic decays B0 s → D+ s Xμ−ν and B0 s → D0 K + Xμ−ν are detected. Two struc- tures are observed in the D0 K + mass spectrum at masses consistent with the known D s1(2536)+ and D∗ s2(2573)+ mesons. The measured branching fractions relative to the total B0 s semileptonic rate are B(B0 s → D∗+ s2 Xμ−ν)/B(B0 s → Xμ−ν) = (3.3 ± 1.0 ± 0.4)%, and B(B0 s → D+ s1 Xμ−ν)/B(B0 s → Xμ−ν) = (5.4 ± 1.2 ± 0.5)%, where the first uncertainty is statistical and the second is systematic. This is the first observation of the D∗+ s2 state in B0 s decays; we also measure its mass and width