Collins-Soper kernel for TMD evolution from lattice QCD

The Collins-Soper kernel relates transverse momentum-dependent parton distribution functions (TMDPDFs) at different energy scales. For small parton transverse momentum q_T∼Λ_QCD, this kernel is nonperturbative and can only be determined with controlled uncertainties through experiment or first-principles calculations. This work presents the first exploratory determination of the Collins-Soper kernel using the lattice formulation of quantum chromodynamics. In a quenched calculation, the N_f=0 kernel is determined at scales in the range 250 MeV <q_T<2 GeV , and an analysis of the remaining systematic uncertainties is undertaken.