Relations among Bc→ J/ψ, ηc form factors

Abstract

We analyze the form factors parametrizing the Bc→ J/ψ, ηc matrix elements of the operators in a generalized low-energy b → c semileptonic Hamiltonian. We consider an expansion in nonrelativistic QCD, classifying the heavy quark spin symmetry breaking terms and expressing the form factors in terms of universal functions in a selected kinematical range. Using as an input the lattice QCD results for the Bc → J/ψ matrix element of the SM operator, we obtain information on other form factors. The extrapolation to the full kinematical range is also presented.