Next-to-leading-logarithm kT resummation for Bc → J/ψ decays

We derive the k(T) resummation for a transverse-momentum-dependent charmonium wave function, which involves the bottom quark mass mb, the charm quark mass m(b), and the charm quark transverse momentum k(T), up to the next-to-leading-logarithm (NLL) accuracy under the hierarchy mb >> m(c) >> k(T). The resultant Sudakov factor is employed in the perturbative QCD (PQCD) approach to the B-c -> J/psi transition form factor A(0)(Bc) (->)( J/psi) (0) and the B-c(+) -> J/psi pi(+) decay. We compare the NLL resummation effect on these processes with the leading-logarithm one in the literature, and find a (5 - 10)% enhancement to the form factor A(0)(Bc) (-> J/psi) (0) and a (10 - 20)% enhancement to the decay rate BR(B-c(+) -> J/psi pi(+)). The improved k(T) resummation formalism is applicable to the PQCD analysis of heavy meson decays to other charmonia. (C) 2020 The Author(s). Published by Elsevier B.V.