Measurement of the Semileptonic Branching Ratio of Bs0 to an Orbitally Excited Ds** State: Br(Bs0→Ds1-(2536)μ+νX)

In a data sample of approximately 1.3fb^-1 collected with the D0 detector between 2002 and 2006, the orbitally excited charm state D_s1^±(2536) has been observed with a measured mass of 2535.7±0.6(stat)±0.5(syst)MeV/c² via the decay mode B_s⁰→D_s1^-(2536)μ⁺ν_μX. A first measurement is made of the branching ratio product Br( bmacr →D_s1^-(2536)μ⁺ν_μX)×Br(D_s1^-→D^*-K_S⁰). Assuming that D_s1^-(2536) production in semileptonic decay is entirely from B_s⁰, an extraction of the semileptonic branching ratio Br(B_s⁰→D_s1^-(2536)μ⁺ν_μX) is made.