Angular analysis of $$ {B}^0\to {D}^{\ast -}{D}_s^{\ast +} $$ with $$ {D}_s^{\ast +}\to {D}_s^{+}\gamma $$ decays

A bstract The first full angular analysis of the $$ {B}^0\to {D}^{\ast -}{D}_s^{\ast +} B 0 → D ∗ − s + decay is performed using 6 fb − 1 pp collision data collected with LHCb experiment at a centre-of-mass energy 13 TeV. {D}_s^{\ast +}\to {D}_s^{+}\gamma γ and D * → {\overline{D}}^0{\pi}^{-} ¯ π vector meson decays are used subsequent {D}_s^{+} K + π {\overline{D}}^0 decays. All helicity amplitudes phases measured, longitudinal polarisation fraction determined to be f L = 0 . 578 ± 010 011 world-best precision, where uncertainty statistical second systematic. pattern amplitude magnitudes found align expectations from quark-helicity conservation in B ratio branching fractions [ℬ( ) × ℬ( )] / measured 2 045 022 071 precision. In addition, observation Cabibbo-suppressed s made significance seven standard deviations. 049 006 003 002, third due limited knowledge fragmentation fractions.