The longitudinal leading-twist distribution amplitude of $J/ψ$ meson within background field theory

Abstract

We make a detailed study on the $J/ψ$ meson longitudinal leading-twist distribution amplitude $ϕ_{2;J/ψ}^\|$ by using the QCD sum rules within the background field theory. By keeping all the non-perturbative condensates up to dimension-six, we obtain accurate QCD sum rules for the moments $\langleξ_{n;J/ψ}^\|\rangle$. The first three ones are $\langleξ_{2;J/ψ}^\|\rangle=0.083(12)$, $\langleξ_{4;J/ψ}^\|\rangle=0.015(5)$ and $\langleξ_{6;J/ψ}^\|\rangle=0.003(2)$, leading to a single peaked behavior for $ϕ_{2;J/ψ}^\|$ which is sharper than the previous ones around the region of $x\sim0.5$. As an application, we adopt the QCD light-cone sum rules to calculate the $B_c$ meson semileptonic decay $B_c^+ \to J/ψ\ell^+ ν_\ell$. We obtain $Γ(B_c^+ \to J/ψ\ell^+ ν_\ell) = (89.67^{+24.76}_{-19.06}) \times 10^{-15}~{\rm GeV}$ and $\Re(J/ψ\ell^+ ν_\ell) = 0.217^{+0.069}_{-0.057}$, which agree with the next-to-leading order pQCD prediction and the new CDF measurement within errors.