Abstract
The first observation of the Bs0 → Ds∗∓K± decay is reported using 3.0 fb−1 of proton-proton collision data collected by the LHCb experiment. The Ds∗∓ mesons are reconstructed through the decay chain Ds∗∓ → γDs∓ (K∓K±π∓). The branching fraction relative to that for Bs0 → Ds∗−π+ decays is measured to be ℬ B s 0 → D s ∗ ∓ K ± / ℬ B s 0 → D s ∗ − π + = 0.068 ± 0.00 5 − 0.002 + 0.003 , $$ \mathrm{\mathcal{B}}\left({B}_s^0\to {D_s^{\ast}}^{\mp }{K}^{\pm}\right)/\mathrm{\mathcal{B}}\left({B}_s^0\to {D_s^{\ast}}^{-}{\pi}^{+}\right)=0.068\pm 0.00{5}_{-0.002}^{+0.003}, $$ where the first uncertainty is statistical and the second is systematic. Using a recent measurement of ℬ B s 0 → D s ∗ − π + $$ \mathrm{\mathcal{B}}\left({B}_s^0\to {D_s^{\ast}}^{-}{\pi}^{+}\right) $$ , the absolute branching fraction of Bs0 → Ds∗∓K± is measured as ℬ B s 0 → D s ∗ ∓ K ± = 16.3 ± 1.2 stat − 0.5 + 0.7 syst ± 4.8 norm × 1 0 − 5 , $$ \mathrm{\mathcal{B}}\left({B}_s^0\to {D_s^{\ast}}^{\mp }{K}^{\pm}\right)=\left(16.3\pm 1.2{\left(\mathrm{stat}\right)}_{-0.5}^{+0.7}\left(\mathrm{syst}\right)\pm 4.8\left(\mathrm{norm}\right)\right)\times 1{0}^{-5}, $$ where the third uncertainty is due to the uncertainty on the branching fraction of the normalisation channel.