First observation of $B^{+} to D_s^{+}K^{+}K^{-}$ decays and a search for $B^{+} to D_s^{+}phi$ decays

A search for $B^{+} to D_s^{+}K^{+}K^{-}$ 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 begin{equation*} mathcal{B}(B^{+} to D_s^{+}K^{+}K^{-} ) = (7.1 pm 0.5 pm 0.6 pm 0.7) times 10^{-6}, end{equation*} where the first uncertainty is statistical, the second systematic and the third due to the uncertainty on the branching fraction of the normalisation mode $B^{+} to D_s^{+} overline{kern -0.2em D}^{0}$. A search is also performed for the pure annihilation decay $B^{+} to D_s^{+}phi$. No significant signal is observed and a limit of begin{equation*} mathcal{B}(B^{+} to D_s^{+}phi) < 4.9 times 10^{-7}~(4.2 times 10^{-7}) end{equation*} is set on the branching fraction at 95$%$ (90$%$) confidence level.