摘要：The recently-proposed quasi distributions point out a promising direction for lattice QCD to investigate the light-cone correlators, such as parton distribution functions (PDF) and distribution amplitudes (DA), directly in the x-space. Owing to its excessive simplicity, the heavy quarkonium can serve as an ideal theoretical laboratory to ascertain certain features of quasi-DA. In the framework of non-relativistic QCD (NRQCD) factorization, we compute the order-αs correction to both light-cone distribution amplitudes (LCDA) and quasi-DA associated with the lowest-lying quarkonia, with the transverse momentum UV cutoff interpreted as the renormalization scale. We confirm analytically that the quasi-DA of a quarkonium does reduce to the respective LCDA in the infinite-momentum limit. We also observe that, provided that the momentum of a charmonium reaches about 2-3 times its mass, the quasi-DAs already converge to the LCDAs to a decent level. These results might provide some useful guidance for the future lattice study of the quasi distributions.
摘要：Inspired by the recent measurements of the ηc meson production at LHC, we investigate the relativistic correction effect for the fragmentation function of the gluon into ηc, which constitutes the crucial nonperturbative elements to understand ηc production at high pT. Employing three distinct methods, we calculate the leading relativistic correction to the g→ηc fragmentation function in the NRQCD factorization framework, as well as verify the existing NLO result for the c→ηc fragmentation function. We also study the evolution behavior of these fragmentation functions with the aid of DGLAP equation.