TMD parton densities in associated real and virtual photon and jet production at LHC

TL;DR

This paper investigates the production of real and virtual photons with jets at the LHC using TMD parton densities, comparing predictions with ATLAS data to improve understanding of proton structure.

Contribution

It introduces a method to determine TMD quark and gluon densities using the $k_T$-factorization approach and compares different models with experimental data.

Findings

Predictions agree with ATLAS data within uncertainties

TMD densities can be constrained with further experimental studies

Inclusion of Z boson exchange improves virtual photon production modeling

Abstract

We study the associated production of real (isolated) or virtual photons (with their subsequent leptonic decay) and hadronic jets in proton-proton collisions at the LHC using the $k_T$-factorization approach of QCD. The consideration is based on the off-shell quark-gluon QCD Compton scattering subprocesses. In the case of virtual photon production, the contributions from Z boson exchange as well as gamma*-Z interference with the full spin correlations are included. The transverse momentum dependent (TMD) quark and gluon densities in a proton are determined from the Kimber-Martin-Ryskin prescription or Catani-Ciafoloni-Fiorani-Marchesini (CCFM) equation. In the latter, we restricted to the case where the gluon-to-quark splitting occurs at the last evolution step and calculate the sea quark density as a convolution of the CCFM-evolved gluon distribution and the TMD gluon-to-quark splitting function. Our numerical predictions are compared with the recent experimental data taken by the ATLAS Collaboration. We discuss the theoretical uncertainties of our calculations and argue that further studies are capable of constraining the TMD parton densities in a proton.