Recent publications by three lattice QCD collaborations have provided an unprecedented wealth of theoretical predictions for the Bq -> Dq* form factors, for spectator flavours q = u/d and q = s. We analyse these predictions within the framework of the heavy-quark expansion (HQE) to order alpha s, 1/mb, and 1/mc2. For the first time, our analysis imposes unitarity bounds for all of the Bq*-> Dq* form factors; this includes newly identified tensor form factors arising in Bq*-> Dq*. This enables us to treat all form factors in the same fashion. At the level of our present analysis, the inclusion of the tensor bounds is not yet constraining the HQE parameter space. We find the lattice QCD results to be well compatible with each other in a joint HQE fit as well as with QCD sum rule estimates that were used in previous HQE analyses. This is in contrast to the strong variability of the posterior predictions, in particular of the form factors ratios R0 and R2. Using the posterior distributions of our HQE analysis, we provide predictions for angular observables and LFU ratios in the Bq -> Dq*l-nu decays.
Challenging B¯s→Ds∗ form factors with the heavy quark expansion
Bordone M.;Jung M.;
2025-01-01
Abstract
Recent publications by three lattice QCD collaborations have provided an unprecedented wealth of theoretical predictions for the Bq -> Dq* form factors, for spectator flavours q = u/d and q = s. We analyse these predictions within the framework of the heavy-quark expansion (HQE) to order alpha s, 1/mb, and 1/mc2. For the first time, our analysis imposes unitarity bounds for all of the Bq*-> Dq* form factors; this includes newly identified tensor form factors arising in Bq*-> Dq*. This enables us to treat all form factors in the same fashion. At the level of our present analysis, the inclusion of the tensor bounds is not yet constraining the HQE parameter space. We find the lattice QCD results to be well compatible with each other in a joint HQE fit as well as with QCD sum rule estimates that were used in previous HQE analyses. This is in contrast to the strong variability of the posterior predictions, in particular of the form factors ratios R0 and R2. Using the posterior distributions of our HQE analysis, we provide predictions for angular observables and LFU ratios in the Bq -> Dq*l-nu decays.
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