$B_c \to B_{s(d)}$ form factors

TL;DR

This paper reports the first lattice QCD calculations of $B_c o B_s$ and $B_c o B_d$ form factors, using multiple lattice spacings and two bottom quark formalisms to ensure reliable results across the entire physical $q^2$ range.

Contribution

It provides the first lattice QCD determination of these form factors, employing two different bottom quark formalisms to validate the results.

Findings

Form factors computed across the entire physical $q^2$ range.

Agreement between NRQCD and heavy-HISQ approaches checked.

Results extrapolated to the physical-continuum limit.

Abstract

We present results of the first lattice QCD calculations of $B_c \to B_s$ and $B_c \to B_d$ weak matrix elements. Results are derived from correlation functions computed on MILC Collaboration gauge configurations with lattice spacings between $0.12$ [fm] and $0.06$ [fm] including 2+1+1 flavours of dynamical sea quarks in the Highly Improved Staggered Quark (HISQ) formalism. Form factors across the entire physical $q^2$ range are then extracted and extrapolated to the physical-continuum limit. Two different formalisms are employed for the bottom quark: non-relativistic QCD (NRQCD) and heavy-HISQ. Checking agreement between these two approaches is an important test of our strategies for heavy quarks on the lattice.