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

## TL;DR

This paper updates the calculation of the B to D* semileptonic form factor at zero recoil using the Oktay-Kronfeld action on HISQ ensembles, providing preliminary results and analyzing valence quark mass dependence.

## Contribution

It introduces an improved lattice QCD calculation of the B to D* form factor at zero recoil using the Oktay-Kronfeld action on new ensembles.

## Key findings

- Preliminary form factor results at two lattice spacings.
- Analysis of valence quark mass dependence.
- Controlled excited state contamination with multistate fits.

## Abstract

We present an update on the calculation of $\bar{B}\to D^\ast \ell \bar{\nu}$ 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 $a\approx 0.12$ and $0.09$ fm and $M_\pi\approx 310$ 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 $a\approx 0.12$ fm ensemble. The excited state is controlled by using multistate fits to the three-point correlators measured at 4--6 source-sink separations.