Z and W production associated with quark-antiquark pair in k_T-factorization at the LHC

TL;DR

The paper addresses $Z$ and $W$ production in association with a quark–antiquark pair within the $k_T$-factorization framework at the LHC. It derives and implements the off-shell matrix element for $g^* g^* \to W/Z q \bar{q}$, employing Sudakov decomposition and the Lipatov vertex, and computes total and differential cross sections using unintegrated gluon densities in CASCADE. By comparing with LO and NLO collinear predictions, the study shows that LO $k_T$-factorization reproduces several higher-order collinear effects, particularly in observables sensitive to the initial-state gluon transverse momenta, while highlighting notable differences in azimuthal and multi-particle kinematics. The results emphasize the importance of the chosen unintegrated parton densities and scale choices for accurate LHC predictions of these processes.

Abstract

We calculate and analyze Z and W production in association with quark-antiquark pair in k_T-factorization. Numerical calculations are performed using the Monte Carlo generator CASCADE for proton proton collisions at LHC energy. We compare total and differential cross sections calculated in k_T-factorization approach with total differential cross sections obtained in LO and NLO calculations in collinear factorization approach. We provide strong evidence that some of the effects of the NLO and even higher order collinear calculation are already included in the LO k_T-factorization calculation.

Figures (18)

• Figure 2.1: Labeling and flow of momenta of the process $pp\to q\,(W/Z)\,\bar{q}\,X$.
• Figure 2.2: Full set of diagrams contributing to $W/Z$ production via off-shell gluon-gluon fusion.
• Figure 2.3: Diagrams contributing to the Lipatov vertex.
• Figure 3.1: Transverse momentum distributions of the produced $Z$ gauge bosons. Calculation with massive $b$-quarks. Both calculations are in LO of perturbation series.
• Figure 3.2: Rapidity distribution of the produced $Z$ gauge bosons. Calculation with massive $b$-quarks. Both calculations are in LO of perturbation series.