Current progress on the semileptonic form factors for $\bar{B} \to D^{\ast} \ell \bar{\nu}$ decay using the Oktay-Kronfeld action

TL;DR

This paper reports progress in calculating semileptonic form factors for B to D* decays using the Oktay-Kronfeld action, employing advanced fitting techniques to obtain preliminary results at zero recoil.

Contribution

It introduces the use of the Oktay-Kronfeld action combined with the Newton and scanning methods for fitting correlation functions in semileptonic decay calculations.

Findings

First reliable results for $h_{A_1}(w)/\rho_{A_1}$ at zero recoil.

Utilization of the Oktay-Kronfeld action for charm and bottom quarks.

Implementation of the Newton method to improve fit stability.

Abstract

We present recent progress in calculating the semileptonic form factors $h_{A_1}(w)$ for the $\bar{B} \to D^{\ast} \ell \bar{\nu}$ decays. We use the Oktay-Kronfeld (OK) action for the charm and bottom valence quarks and the HISQ action for light quarks. We adopt the Newton method combined with the scanning method to find a good initial guess for the $\chi^2$ minimizer in the fitting of the 2pt correlation functions. The main advantage is that the Newton method lets us to consume all the time slices allowed by the physical positivity. We report the first, reliable, but preliminary results for $h_{A_1}(w)/\rho_{A_1}$ at zero recoil ($w=1$). Here we use a MILC HISQ ensemble ($a = 0.12$ fm, $M_{\pi}$ = 220 MeV, and $N_f = 2 + 1 + 1$ flavors).