First observation of (B)over-bar(s)(0) -> D-s2*X+mu(-)(nu)over-bar decays

Using data collected with the LHCb detector in proton-proton collisions at a centre-of-mass energy of 7 TeV, the semileptonic decays (B) over bar (0)(s) -> D+X mu(-)(nu) over bar and (B) over bar (0)(s) -> (DK+X)-K-0 mu(-)(nu) over bar are detected. Two structures are observed in the (DK+)-K-0 mass spectrum at masses consistent with the known D-s1(2536)(+) and D-s2*(2573)(+) mesons. The measured branching fractions relative to the total (B) over bar (0)(s) semileptonic rate are B((B) over bar (0)(s) -> (Ds2X)-X-*mu(-)(nu) over bar /B(B-2(-0) -> X mu(-)(nu) over bar) = (3.3 +/- 1.0 +/- 0.4)%, and B((B) over bar (0)(s) -> (Ds2X)-X-*mu(-)(nu) over bar /B(B-2(-0) -> X mu(-)(nu) over bar) = (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 B-s2*(+) decays; we also measure its mass and width. (C) 2011 CERN. Published by Elsevier B.V. All rights reserved. RI Muresan, Raluca-Anca/C-3725-2011; Vazquez Regueiro, Pablo/F-7610-2010; Galli, Domenico/A-1606-2012; Murtas, Fabrizio/B-5729-2012; Popovici, Bogdan/B-6521-2012; Zhang, Liming/B-8122-2012; Patrignani, Claudia/C-5223-2009; Coca, Cornelia/B-6015-2012; Eklund, Lars/C-7709-2012; Carbone, Angelo/C-8289-2012; Soler, Paul/E-8464-2011; Merkin, Mikhail/D-6809-2012; Leflat, Alexander/D-7284-2012; Petrolini, Alessandro/H-3782-2011; Sarti, Alessio/I-2833-2012