Measurement of the underlying event in jet events from 7 TeV proton-proton collisions with the ATLAS detector

Abstract

Distributions sensitive to the underlying event in QCD jet events have been measured with the ATLAS detector at the LHC, based on 37/pb of proton-proton collision data collected at a centre-of-mass energy of 7 TeV. Charged-particle mean $p_T$ and densities of all-particle $E_T$ and charged-particle multiplicity and $p_T$ have been measured in regions azimuthally transverse to the hardest jet in each event. These are presented both as one-dimensional distributions and with their mean values as functions of the leading-jet transverse momentum from 20 GeV to 800 GeV. The correlation of charged-particle mean $p_T$ with charged-particle multiplicity is also studied, and the $E_T$ densities include the forward rapidity region; these features provide extra data constraints for Monte Carlo modelling of colour reconnection and beam-remnant effects respectively. For the first time, underlying event observables have been computed separately for inclusive jet and exclusive dijet event selections, allowing more detailed study of the interplay of multiple partonic scattering and QCD radiation contributions to the underlying event. Comparisons to the predictions of different Monte Carlo models show a need for further model tuning, but the standard approach is found to generally reproduce the features of the underlying event in both types of event selection.

17 pages plus author list + cover pages (31 pages total), 6 figures, 3 tables, submitted to European Physical Journal C, All figures including auxiliary figures are available at http://atlas.web.cern.ch/Atlas/GROUPS/PHYSICS/PAPERS/STDM-2011-31/

References in corpus (9)

• PYTHIA 6.4 Physics and Manual
• New parton distributions for collider physics
• Herwig++ Physics and Manual
• Parton Distributions for LO Generators
• Measurement of the underlying event in the Drell-Yan process in proton-proton collisions at sqrt(s) = 7 TeV
• CT10 parton distributions and other developments in the global QCD analysis
• Diffraction and correlations at the LHC: definitions and observables
• Generation cuts and Born suppression in POWHEG
• Imagiro: an implementation of Bayesian iterative unfolding for high energy physics

Cited by in corpus (3)

• Effects of color reconnection on $t\bar{t}$ final states at the LHC
• Measurement of distributions sensitive to the underlying event in inclusive Z-boson production in $pp$ collisions at $\sqrt{s}=7$ TeV with the ATLAS detector
• Double Parton Scattering, Multi-Parton Interactions, underlying event and identified hadrons: summary of recent results