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

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 $B_c\to J/\psi$.