Longitudinal leading-twist distribution amplitude of the J/psi meson within the background field theory

We make a detailed study on the J/psi meson longitudinal leading- twist distribution amplitude phi(2;J/psi) (parallel to) by using the QCD sum rules within the background field theory. By keeping all the nonperturbative condensates up to dimension 6, we obtain accurate QCD sum rules for the moments The first three ones are = 0.083(12), = 0.015(5), and = 0.003(2), respectively. Those values indicate a single peaked behavior for phi(parallel to)(2;J/psi). As an application, we adopt the QCD light-cone sum rules to calculate the B-c meson semileptonic decay B-c(+) -> J/psi rho(+)nu rho. We obtain Gamma(B-c(+) -> J/psi rho(+)nu rho) = (89.67(-19.06)(vertical bar 24.76) x 10(-15) GeV and eta(J/psi rho(+)nu rho) = 0.217(vertical bar 0.069) (-0.057), which agree with both the extrapolated next- to- leading order pQCD prediction and the new CDF measurement within errors.