Evidence for B- -> D(s)(+)K(-)l(-)(nu)over-bar(l) and search for B- -> D-s*(+)K(-)l(-)(nu)over-bar(l)

Abstract

We report measurements of the decays B- -> D-s(()*()+)K(-)l(-)(nu) over bar (l) in a data sample containing 657 X 10(6)B (B) over bar pairs collected with the Belle detector at the KEKB asymmetric-energy e(+)e(-) collider. We observe a signal with a significance of 6 sigma for the combined D-s and D-s* modes and find the first evidence of the B- -> D(s)(+)K(-)l(-)(nu) over bar (l) decay with a significance of 3.4 sigma. We measure the following branching fractions: B(B- -> D(s)(+)K(-)l(-)(nu) over bar (l)) (0.30 +/- 0.09(stat)(-0.08)(+0.11) (syst) X 10(-3) and B(B- -> D-s(()*()+)K(-)l(-)(nu) over bar (l)) 0.59 +/- 0.12(stat) +/- 0.15(syst)) X 10(-3) and set an upper limit B(B- -> D-s*(+)K(-)l(-)(nu) over bar (l)) = 0.5 X 10(-3) at the 90% confidence level. We also present the first measurement of the Ds+K- invariant mass distribution in these decays, which is dominated by a prominent peak around 2.6 GeV/c(2).