Speaker
Description
We discuss the treatment of finite charm and bottom quark mass effects in the Collins-Soper kernel or equivalently the rapidity anomalous dimension. In particular, we derive a consistent flavor matching relation with different numbers of active flavors. This allows us to properly separate the perturbative contributions due to heavy quarks from the remaining $n_F = 3$ massless contributions. Our results allow for the first time for a fully consistent comparison with the $n_F = 3$ lattice determinations of the Collins-Soper kernel in order to determine its non-perturbative contributions at large distances. We also discuss the corresponding impact of the mass effects and correct treatment of flavor thresholds in the evolution kernel at the level of the resummed $q_T$ spectrum.