2025/03/19 by Judd Harrison, Harrison, Judd
Physics and Astronomy · #FOS: Physical sciences #High Energy Physics - Lattice (hep-lat) #High Energy Physics - Phenomenology (hep-ph) #High-Energy Particle Collisions Research #Particle physics theoretical and experimental studies #Quantum Chromodynamics and Particle Interactions
paper · pdf · doi:10.48550/arxiv.2503.15090
openalex publication_date 2025/03/19 · openalex created_date 2025/10/10 · openalex updated_date 2026/08/02
We present an update of HPQCD's lattice QCD determination of the Bc→ J/ψ vector and axial-vector form factors, and provide 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 nf=2+1+1 HISQ gluon field configurations. This calculation includes two additional ensembles, one with physically light up and down quarks and a≈ 0.06 fm and one with a≈ 0.03fm 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. We use our recent results for the heavy-charm susceptibilities, as a function of u=mc/mh, in order to employ the full dispersive parameterisation for Bc→ J/ψ in our physical-continuum extrapolation. We give updated SM predictions R(J/ψ)=0.2597(27), Aλτ=0.5093(42), FLJ/ψ=0.4421(55), and AFB=-0.0567(61), reducing uncertainties by 29%, 45%, 40% and 50% respectively. Since our lattice form factors cover the full kinematic range we can use them to test extrapolations using data in a truncated range, at low-recoil. We investigate different physical continuum parameterisation schemes, with lattice results in the first 1/3 of the kinematic range near q2max. We find that unexpectedly large systematic uncertainties near q2=0 can emerge when extrapolating synthetic data in the high-q2 region if higher order kinematical terms are omitted from the physical continuum extrapolation. This suggests a potentially underestimated systematic uncerainty entering extrapolations of synthetic lattice QCD data for the related B→ D^*ℓν decay from the high-q2 region into the low-q2 region.