Collins-Soper kernel from lattice QCD at the physical pion mass

This work presents a determination of the quark Collins-Soper kernel, which relates transversemomentum-dependent parton distributions at different rapidity scales, using lattice QCD. This is the first lattice QCD calculation of the kernel at quark masses corresponding to a close-to-physical value of the pion mass, with next-to-next-to-leading logarithmic matching to transverse-momentum-dependent parton distributions from the corresponding lattice-calculable distributions, and includes a complete analysis of systematic uncertainties arising from operator mixing. The kernel is extracted at transverse momentum scales 240 MeV less than or similar to q(T) less than or similar to 1.6 GeV with a precision sufficient to begin to discriminate between different phenomenological models in the nonperturbative region.