First observation and measurement of the branching fraction for the decay B {/s 0} → D {/s ∗} ∓ K ±

Abstract

The first observation of the B0 s → D∗∓ s K± decay is reported using 3.0 fb−1 of protonproton collision data collected by the LHCb experiment. The D∗∓ s mesons are reconstructed through the decay chain D∗∓ s → γD∓ s (K∓K±π ∓). The branching fraction relative to that for B0 s → D∗− s π + decays is measured to be B(B0 s→ D∗∓ s K±)/B(B0 s→ D∗− s π +) = 0.068 ± 0.005+0.003 −0.002, where the first uncertainty is statistical and the second is systematic. Using a recent measurement of B(B0 s → D∗− s π +), the absolute branching fraction of B0 s → D∗∓ s K± is measured as B(B0 s → D∗∓ s K±) = ( 16.3 ± 1.2 (stat) +0.7 −0.5 (syst) ± 4.8 (norm) ) × 10−5 , where the third uncertainty is due to the uncertainty on the branching fraction of the normalisation channel.