Relations among $B_c\to J/\ddot{I}ˆ,\hat{I}{\cdot }_c$ form factors

Abstract

We analyze the form factors parametrizing the $B_c\to J/\ddot{I}ˆ,\hat{I}{\cdot }_c$ matrix elements of the operators in a generalized low-energy $b\to c$ 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 $B_c\to J/\ddot{I}ˆ$ matrix element of the SM operator, we obtain information on other form factors. The extrapolation to the full kinematical range is also presented.

32 pages, 4 figures. To appear in JHEP