Semileptonic transitions: B(s) → π(K); Ds → K; D → π, K; and K → π

Continuum Schwinger function methods for the strong-interaction bound-state problem are used to arrive at a unified set of parameter-free predictions for the semileptonic K -> pi, D -> pi, K and D-s -> K, B-(s) -> pi(K) transition form factors and the associated branching fractions. The form factors are a leading source of uncertainty in all such calculations: our results agree quantitatively with available data and provide benchmarks for the hitherto unmeasured D-s -> K-0, (B) over bar (s) -> K+ form factors. The analysis delivers a value of vertical bar V-cs vertical bar = 0.974(10) and also predictions for all branching fraction ratios in the pseudoscalar meson sector that can be used to test lepton flavour universality. Quantitative comparisons are provided between extant theory and the recent measurement of BBs0 -> K-mu+nu mu. Here, further, refined measurements would be useful in moving toward a more accurate value of vertical bar V-ub vertical bar. (C) 2021 The Author(s). Published by Elsevier B.V.

Automated summary

Continuum Schwinger function methods are used to predict transition form factors and branching fractions in the strong-interaction bound-state problem. The results agree with available data and provide benchmarks for unmeasured form factors. The study also predicts values for V-cs vertical bar and branching fraction ratios, which can be used to test lepton flavour universality. Quantitative comparisons are made with recent experimental measurements, emphasizing the importance of further refinements.