Correlations in Double Parton Distributions: Perturbative and Non-Perturbative effects

TL;DR

This paper investigates double parton distribution functions (dPDFs) for Double Parton Scattering at the LHC, revealing the significance of correlations and the limitations of factorized models, with implications for experimental studies.

Contribution

It combines a Light-Front constituent quark model with QCD evolution to analyze correlations in dPDFs, highlighting their impact at LHC energies and the failure of simple factorized approximations.

Findings

Factorized dPDFs fail in the valence region.

Gluon-gluon correlations can be as large as 20%.

Correlations are influenced by non-perturbative and perturbative effects.

Abstract

The correct description of Double Parton Scattering (DPS), which represents a background in several channels for the search of new Physics at the LHC, requires the knowledge of double parton distribution functions (dPDFs). These quantities represent also a novel tool for the study of the three-dimensional nucleon structure, complementary to the possibilities offered by electromagnetic probes. In this paper we analyze dPDFs using Poincar\'e covariant predictions obtained by using a Light-Front constituent quark model proposed in a recent paper, and QCD evolution. We study to what extent factorized expressions for dPDFs, which neglect, at least in part, two-parton correlations, can be used. We show that they fail in reproducing the calculated dPDFs, in particular in the valence region. Actually measurable processes at existing facilities occur at low longitudinal momenta of the interacting partons; to have contact with these processes we have analyzed correlations between pairs of partons of different kind, finding that, in some cases, they are strongly suppressed at low longitudinal momenta, while for other distributions they can be sizeable. For example, the effect of gluon-gluon correlations can be as large as 20 $\%$. We have shown that these behaviors can be understood in terms of a delicate interference of non-perturbative correlations, generated by the dynamics of the model, and perturbative ones, generated by the model independent evolution procedure. Our analysis shows that at LHC kinematics two-parton correlations can be relevant in DPS, and therefore we address the possibility to study them experimentally.