Implications of Heavy Quark Spin Symmetry and NRQCD on B_c → J/ψ, η_c form factors

Abstract

We discuss the analysis of Bc → J/ψ, ηc form factors, based on the heavy quark spin symmetry and nonrelativistic QCD (NRQCD) performed in Ref. [1]. We perform an expansion on the inverse of the heavy quarks’ masses using power counting rules of NRQCD up to the next-to-leading order. This allows us to classify the heavy quark spin symmetry-breaking terms and express the form factors in terms of universal functions in a selected kinematical range. Using as input the lattice QCD results for the Bc → J/ψ matrix element of the SM operator, we obtain information on other form factors.