First observation of B¯s0→Ds2⁎+Xμ−ν¯ 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 B ¯ s 0 → D s + X μ − ν ¯ and B ¯ s 0 → D 0 K + X μ − ν ¯ are detected. Two structures are observed in the D 0 K + mass spectrum at masses consistent with the known D s 1 ( 2536 ) + and D s 2 ⁎ ( 2573 ) + mesons. The measured branching fractions relative to the total B ¯ s 0 semileptonic rate are B ( B ¯ s 0 → D s 2 ⁎ + X μ − ν ¯ ) / B ( B ¯ s 0 → X μ − ν ¯ ) = ( 3.3 ± 1.0 ± 0.4 ) % , and B ( B ¯ s 0 → D s 1 + X μ − ν ¯ ) / B ( B ¯ s 0 → X μ − 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 s 2 ⁎ + state in B ¯ s 0 decays; we also measure its mass and width.