2023/04/06 by Harrison, Judd, Davies, Christine T. H.
#FOS: Physical sciences #High Energy Physics - Lattice (hep-lat) #High Energy Physics - Phenomenology (hep-ph)
paper · doi:10.48550/arxiv.2304.03137
We compute the complete set of SM and tensor B(s)→ D(s)^*ℓν semileptonic form factors across the full kinematic range of the decay using second generation MILC nf=2+1+1 HISQ gluon field configurations and HISQ valence quarks, with the heavy-HISQ method. Lattice spacings range from 0.09fm to 0.044fm with pion masses from ≈ 300MeV down to the physical value and heavy quark masses ranging between ≈ 1.5 mc and 4.1 mc ≈ 0.9 mb; currents are normalised nonperturbatively. Using the recent B(s)→ D^*(s)ℓν_ℓ data from Belle and LHCb together with our form factors we determine a model independent value of Vcb=39.03(56)exp(67)latt× 10-3, in agreement with previous exclusive determinations and in tension with the inclusive result at the level of 3.6σ. We observe a ≈ 1σ tension between the shape of the differential decay rates computed using our form factors and those measured by Belle. We compute a lattice-only SM value for the ratio of semitauonic and semimuonic decay rates, R(D^*)=0.273(15), which we find to be closer to the recent Belle measurement and HFLAV average than theory predictions using fits to experimental differential rate data for B→ D^*ℓν_ℓ. Determining Vcb using the total rate for B→ D^*ℓν gives a value in agreement with inclusive results. We compute the longitudinal polarisation fraction for the semitauonic mode, FLD^*=0.395(24), which is in tension at the level of 2.2σ with the recent Belle measurement. Our calculation combines B→ D^* and Bs→ Ds^* lattice results, and we provide an update which supersedes our previous lattice computation of the Bs→ Ds^* form factors. We also give the chiral perturbation theory needed to analyse the tensor form factors.