$B_c \to J /\psi$ tensor form factors at large momentum recoil

We present a next-to-leading order (NLO) relativistic correction to Bc → J/ψ tensor form factors within nonrelativistic QCD (NRQCD). We also consider complete Dirac bilinears cΓb with 4 × 4 matrices Γ = 1,γ5,γμ,γμγ5,σμν in the b → c transition. The relation among different current form factors is given and it shows that symmetries emerge in the heavy bottom quark limit. For a phenomenological extension, we propose to extract the long-distance matrix elements (LDMEs) for Bc meson from the recent HPQCD lattice data and the NLO form factors at large momentum recoil.