Studying the Underlying Event in Drell-Yan and High Transverse Momentum Jet Production at the Tevatron

TL;DR

This study analyzes the underlying event in proton-antiproton collisions at the Tevatron, using charged particle behavior associated with jets and Drell-Yan pairs to test and improve QCD Monte-Carlo models.

Contribution

It introduces a detailed method to characterize the underlying event in different regions of phase space, providing data to refine QCD Monte-Carlo simulations.

Findings

Transverse region is highly sensitive to the underlying event.

Data corrected to particle level for model comparison.

Separation of hard and soft components in jet production.

Abstract

We study the underlying event in proton-antiproton collisions by examining the behavior of charged particles (transverse momentum pT > 0.5 GeV/c, pseudorapidity |\eta| < 1) produced in association with large transverse momentum jets (~2.2 fb-1) or with Drell-Yan lepton-pairs (~2.7 fb-1) in the Z-boson mass region (70 < M(pair) < 110 GeV/c2) as measured by CDF at 1.96 TeV center-of-mass energy. We use the direction of the lepton-pair (in Drell-Yan production) or the leading jet (in high-pT jet production) in each event to define three regions of \eta-\phi space; toward, away, and transverse, where \phi is the azimuthal scattering angle. For Drell-Yan production (excluding the leptons) both the toward and transverse regions are very sensitive to the underlying event. In high-pT jet production the transverse region is very sensitive to the underlying event and is separated into a MAX and MIN transverse region, which helps separate the hard component (initial and final-state radiation) from the beam-beam remnant and multiple parton interaction components of the scattering. The data are corrected to the particle level to remove detector effects and are then compared with several QCD Monte-Carlo models. The goal of this analysis is to provide data that can be used to test and improve the QCD Monte-Carlo models of the underlying event that are used to simulate hadron-hadron collisions.