Intrinsic $k_T$ and soft gluons in Monte Carlo event generators

TL;DR

This paper examines how intrinsic transverse momentum ($k_T$) and soft gluons influence measurements in Monte Carlo event generators, emphasizing the importance of non-perturbative effects and uncertainty treatment in TMD fits.

Contribution

It compares intrinsic $k_T$ determinations across TMD and collinear Monte Carlo approaches, highlighting the role of soft-gluon scales and correlated uncertainties.

Findings

Soft-gluon resolution scale impacts $k_T$ extraction.

Proper uncertainty treatment is crucial for accurate TMD fits.

Intrinsic $k_T$ varies with rapidity region.

Abstract

Experimental measurements of the transverse momentum of Drell-Yan lepton pairs are sensitive to non-perturbative physics associated with the intrinsic parton transverse momentum $k_T$. We discuss recent determinations of intrinsic $k_T$ in the context of transverse momentum dependent (TMD) parton branching calculations and collinear parton-shower Monte Carlo generators. We illustrate the influence of the soft-gluon resolution scale and the non-perturbative Sudakov region on the intrinsic $k_T$ extraction. We emphasize the relevance of the correct treatment of correlated uncertainties between different transverse momentum bins in TMD fits and present an application to the determination of the intrinsic $k_T$ in the forward rapidity region.