A validity check of the KATIE parton level event generator in the $k_t$-factorization and collinear frameworks

TL;DR

This paper evaluates the extsc{KaTie} event generator's accuracy in calculating cross sections for ep and p-p collisions within $k_t$-factorization and collinear frameworks, identifying and fixing a transformation bug to improve data agreement.

Contribution

The study identifies a bug in extsc{KaTie} affecting ep data and demonstrates how fixing it enables accurate predictions aligned with experimental results.

Findings

Fixing the lab to Breit transformation improves ep dijet cross section predictions.

MRW NLO UPDFs with angular ordering successfully predict ATLAS Drell-Yan data.

$k_t$-factorization is effective at small parton momenta and high energies.

Abstract

In the present paper, we check and study the validity of the \textsc{KaTie} parton level event generator, by calculating the inclusive electron-proton (ep) dijet and the Proton-proton (p-p) Drell-Yan electron-pair productions differential cross sections in the $k_t$- and collinear factorization frameworks. The Martin-Ryskin-Watt (MRW) unintegrated parton distribution functions (UPDFs) are used as the input UPDFs. The results are compared with those of ZEUS ep inclusive dijet and ATLAS p-p Drell-Yan electron-pair productions, experimental data. The \textsc{KaTie} parton level event generator can directly calculate the cross sections in the $k_t$-factorization framework. It is noticed that the lab to the Breit transformation in this generator is not correctly implemented by its author, so the produced output does not cover the ep ZEUS experimental data in which the mentioned transformation is applied. By fixing the above transformation in the \textsc{KaTie} generator code, we could appropriately produce the ep inclusive dijet differential cross section, in comparison with those of ZEUS data. It is also shown that the MRW at the NLO level, with the angular ordering constraint can successfully predict the ATLAS p-p Drell-Yan data. Finally, as it is expected, we conclude that the $k_t$-factorization is an appropriate tool for the small longitudinal parton momenta and high center of mass energies, with respect to the collinear one.