Semileptonic B_c-meson decays in sum rules of QCD and NRQCD

TL;DR

This paper investigates semileptonic B_c-meson decays into heavy quarkonia using QCD and NRQCD sum rules, deriving form factors and calculating decay widths with improved stability and reliability.

Contribution

It provides analytical expressions for spectral densities, derives relations for form factors via spin symmetry, and includes gluon condensate corrections, enhancing the sum rule method's accuracy.

Findings

Derived form factors using spin symmetry in NRQCD.

Calculated decay widths for B_c to J/ψ and η_c transitions.

Included gluon condensate corrections, improving result stability.

Abstract

The semileptonic B_c-meson decays into the heavy quarkonia J/\psi (\eta_c) and a pair of leptons are investigated in the framework of three-point sum rules of QCD and NRQCD. Calculations of analytical expressions for the spectral densities of QCD and NRQCD correlators with account for the Coulomb-like \alpha_s/v terms are presented. The generalized relations due to the spin symmetry of NRQCD for the form factors of B_c\to J/\psi (\eta_c)l\nu_l transitions with l denoting one of the leptons e, \mu or \tau, are derived at the recoil momentum close to zero. This allows one to express all NRQCD form factors through a single universal quantity, an analogue of Isgur-Wise function at the maximal invariant mass of lepton pair. The gluon condensate corrections to three-point functions are calculated both in full QCD in the Borel transform scheme and in NRQCD in the moment scheme. This enlarges the parameteric stability region of sum rule method, that makes the results of the approach to be more reliable. Numerical estimates of widths for the transitions of B_c\to J/\psi (\eta_c)l\nu_l are presented.