Lattice QCD calculation of the Collins-Soper kernel from quasi-TMDPDFs
Phiala E. Shanahan, Michael L. Wagman, Yong Zhao
Abstract
This work presents a lattice quantum chromodynamics (QCD) calculation of the nonperturbative Collins-Soper kernel, which describes the rapidity evolution of quark transverse-momentum-dependent parton distribution functions. The kernel is extracted at transverse momentum scales in the range $400\text{ }\text{ }\mathrm{MeV}<{q}_{T}<1.7\text{ }\text{ }\mathrm{GeV}$ in a calculation with dynamical fermions and quark masses corresponding to a larger-than-physical pion mass, ${m}_{\ensuremath{\pi}}=538(1)\text{ }\text{ }\mathrm{MeV}$. It is found that different approaches to extract the Collins-Soper kernel from the same underlying lattice QCD matrix elements yield significantly different results and uncertainty estimates, revealing that power corrections, such as those associated with higher-twist effects, and perturbative matching between quasi- and light-cone beam functions, cannot be neglected.