Limits of TMD evolution in SIDIS at moderate Q

Leonard Gamberg,U D’Alesio,F Murgia

doi:10.1051/epjconf/20158502002

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 .

Highlights

TMD factorization separates a transversely differential cross section into a perturbatively calculable part and several well-defined universal factors [1], including the transverse momentum parton distribution functions fragmentation functions
The TMD factorization theorems for semi-inclusive deep inelastic scattering (SIDIS) is schematically: dσSIDIS = H f,SIDIS(αs(μ), μ/Q) ⊗ F f /H1 (x, k1T ; μ, ζ1)
Where similar expressions hold for Drell-Yan scattering (DY), and inclusive e+e− annihilation into back-to-back hadrons (e+e− → H1 + H2 + X)

Summary

Introduction

TMD factorization separates a transversely differential cross section into a perturbatively calculable part and several well-defined universal factors [1], including the transverse momentum parton distribution functions fragmentation functions. The latter are interpreted in terms of hadronic structure. The COMPASS experiment has released data [6] for charged hadron SIDIS measurements that are differential in all kinematical parameters and cover a range of moderately low values of Q. We will use this to study the Q dependence in the region. While the range in Q in Ref. [6] is too small to allow for reasonably accurate fits to the nonperturbative evolution, it is significant enough that we can use it to rule out any dramatic variations with Q that might be suggested by direct direct extrapolations from large Q fits, and to infer certain general aspects of the very large coordinate space Q dependence [7]

TMD Evolution

Empirical Evolution at Moderate Q

Comparison with TMD Evolution

Modified Large bT Behavior