Update on $B \to D^\ast \ell \nu$ form factor at zero-recoil using the Oktay-Kronfeld action

Abstract

We present an update on the calculation ofB → D * ν semileptonic form factor at zero recoil using the Oktay-Kronfeld bottom and charm quarks on N f = 2+1+1 flavor HISQ ensembles generated by the MILC collaboration. Preliminary results are given for two ensembles with a ≈ 0.12 and 0.09 fm and M π ≈ 310 MeV. Calculations have been done with a number of valence quark masses, and the dependence of the form factor on them is investigated on the a ≈ 0.12 fm ensemble. The excited state is controlled by using multistate fits to the three-point correlators measured at 4-6 source-sink separations.

Lattice $B \to D^{(*)}$ form factors, $R(D^{(*)})$, and $|V_{cb}|$

“…The LANL/SWME collaboration have also released preliminary results for the h A 1 form factor at zero recoil [38,39], and at this conference [40]. Their calculation is carried out on the n f = 2 + 1 + 1 MILC HISQ ensembles, using the Oktay-Kronfeld (OK) action [41,42] for valence charm and bottom, at two lattice spacings a ≈ 0.12, 0.09 fm and a single pion mass m π ≈ 310 MeV.…”

“…FNAL/MILC '14 HPQCD '18 HPQCD '18, Figure 7: Results for B → D * at zero recoil from LANL/SWME [39] showing the effect of higher orders of current improvement (left) and compared with prior results in the literature (right) -Note that ρ A 1 is here set to 1 so the comparison is only indicative. Belle data [20,21] using different parameterisations (colored bands) [19,1] and predictions of HQET.…”