A model of non-perturbative gluon emission in an initial state parton shower

TL;DR

This work introduces a non-perturbative extension to the initial-state parton shower to smear transverse momentum throughout perturbative evolution, implemented via a low-$p_ op$ modification to the strong coupling. Two simple NP forms (flat and quadratic) controlled by $p_{ op 0}$ and $varphi_0$ are tested against Tevatron, fixed-target, and ISR data, with a quadratic form providing the best parton-level fit at $p_{ op 0} o0.75$ GeV and $alpha_S(0)=0$. Hadron-level results, which include standard hadronization masses, require different NP parameters and reveal tension across data sets, though NP-only input can improve compatibility, suggesting potential benefits from combining with final-state modeling. The model extrapolates to LHC energies and is compared to ResBos and Gaussian intrinsic-$k_ op$ approaches, predicting a similar peak position but different high-$p_ op$ behavior, indicating a plausible universal mechanism for non-perturbative soft gluon radiation with important implications for precision W/Z and Higgs phenomenology.

Abstract

We consider a model of transverse momentum production in which non-perturbative smearing takes place throughout the perturbative evolution, by a simple modification to an initial state parton shower algorithm. Using this as the important non-perturbative ingredient, we get a good fit to data over a wide range of energy. Combining it with the non-perturbative masses and cutoffs that are a feature of conventional parton showers also leads to a reasonable fit. We discuss the extrapolation to the LHC.