Measurement of the underlying-event properties with the ATLAS detector

TL;DR

This paper measures underlying event properties in proton-proton collisions at 7 TeV and 13 TeV using ATLAS data, comparing results with various Monte Carlo generator predictions to improve modeling accuracy.

Contribution

It provides new measurements of event-shape variables and charged particle distributions in Drell-Yan events at 7 TeV and 13 TeV, enhancing understanding of underlying event modeling.

Findings

Distributions of topological event-shape variables are measured and compared with MC predictions.

First study of charged particle multiplicity and transverse momentum sum as functions of kinematic variables at 13 TeV.

Results show discrepancies between data and some MC models, guiding future improvements.

Abstract

A correct modelling of the underlying event in proton-proton collisions is important for the proper simulation of kinematic distributions of high-energy collisions. The ATLAS collaboration extended previous studies at 7 TeV with a leading track or jet or Z boson by a new study of Drell-Yan events in 1.1 1/fb of data collected at a center-of-mass energy of 7 TeV. In this new study the distributions of several topological event-shape variables based on charged particles are measured, both integrated and differential in the transverse momentum of the Drell-Yan lepton pair. These measurements are sensitive to the underlying-event as well as the onset of hard emissions. The results have been compared with the predictions of several state-of-the-art MC generators. The collaboration has also performed a first study of the number and transverse momentum sum of charged particles as a function of transverse momentum and azimuthal angle in a special data set taken with low beam currents at a center-of-mass energy of 13 TeV. The results are compared to predictions of several MC generators.