Limits of TMD evolution in SIDIS at moderate Q

Abstract

We investigate semi-inclusive deep inelastic scattering measurements in the region of relatively small Q, where sensitivity to nonperturbative transverse momentum dependence can dominate the evolution. Using SIDIS data from the COMPASS experiment, we find that regions of coordinate space that dominate in TMD processes when the hard scale is of the order of only a few GeV are much larger than those commonly probed in large Q measurements. This suggests that the details of nonperturbative effects in TMD evolution are especially significant in the region of intermediate Q. We emphasize the strongly universal nature of the nonperturbative component of evolution. and its potential to be tightly constrained by fits from a wide variety of observables that include both large and moderate Q.