First observation of B + → D s + K + K − decays and a search for B + → D s + ϕ decays

Abstract A search for B + → D s + K + K − decays is performed using pp collision data corresponding to an integrated luminosity of 4.8 fb−1, collected at centre-of-mass energies of 7, 8 and 13 TeV with the LHCb experiment. A significant signal is observed for the first time and the branching fraction is determined to be ℬ B + → D s + K + K − = 7.1 ± 0.5 ± 0.6 ± 0.7 × 1 0 − 6 , $$ \mathrm{\mathcal{B}}\left({B}^{+}\to {D}_s^{+}{K}^{+}{K}^{-}\right)=\left(7.1 \pm 0.5 \pm 0.6 \pm 0.7\right)\times 1{0}^{-6}, $$ where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fraction of the normalisation mode B+→Ds+D¯0 $$ {B}^{+}\to {D}_s^{+}{\overline{D}}^0 $$. A search is also performed for the pure annihilation decay B + → D s + ϕ. No significant signal is observed and a limit of ℬ B + → D s + ϕ < 4.9 × 1 0 − 7 4.2 × 1 0 − 7 $$ \mathrm{\mathcal{B}}\left({B}^{+}\to {D}_s^{+}\phi \right)