Measurement of the branching fraction of the $${{B} ^0} {\rightarrow }{{D} ^+_{s}} {{\pi } ^-} $$ decay

A branching fraction measurement of the B 0 → D + s π − decay is presented using proton–proton collision data collected with the LHCb experiment, corresponding to an integrated luminosity of 5 . 0 fb − 1 . The branching fraction is found to be B ( B 0 → D + s π − ) = ( 19 . 4 ± 1 . 8 ± 1 . 3 ± 1 . 2 ) × 10 − 6 , where the first uncertainty is statistical, the second systematic and the third is due to the uncertainty on the B 0 → D − π + , D + s → K + K − π + and D − → K + π − π − branching fractions. This is the most precise single measurement of this quantity to date. As this decay proceeds through a single amplitude involving a b → u charged-current transition, the result provides information on non-factorisable strong interaction effects and the magnitude of the Cabibbo–Kobayashi–Maskawa matrix element V ub . Additionally, the collision energy dependence of the hadronisation-fraction ratio f s / f d is measured through B 0 s → D + s π − and B 0 → D − π + decays.