Update of HPQCD $B_c\to J/\psi$ Form Factors

TL;DR

This paper updates lattice QCD calculations of $B_c o J/$ form factors, including tensor form factors, using improved methods and new ensembles to enhance accuracy across the full decay kinematic range.

Contribution

It provides the first comprehensive lattice QCD determination of $B_c o J/$ form factors including tensor form factors with physical quark masses and continuum extrapolation.

Findings

Accurate form factors across the full kinematic range.

Inclusion of tensor form factors in the analysis.

Use of physical light quark masses and fine lattice spacings.

Abstract

We present an update of our lattice QCD determination of the $B_c\to J/\psi$ vector and axial-vector form factors, including new results for the tensor form factors. We use the Highly Improved Staggered Quark action for all valence quarks, together with the second generation MILC $n_f=2+1+1$ HISQ gluon field configurations. This calculation includes two additional ensembles, one with physically light up and down quarks and $a\approx 0.06 \mathrm{fm}$ and one with $a\approx 0.03\mathrm{fm}$ on which we are able to reach the physical bottom quark mass. Our calculation uses nonperturbatively renormalised current operators and covers the full kinematical range of the decay. Our physical-continuum extrapolation utilises the full dispersive parameterisation for $B_c\to J/\psi$.