Measurement of charged-particle event shape variables in sqrt(s) = 7 TeV proton-proton interactions with the ATLAS detector

TL;DR

This paper reports measurements of charged-particle event shape variables in 7 TeV proton-proton collisions at the LHC using the ATLAS detector, revealing discrepancies with Monte Carlo predictions.

Contribution

First measurement of charged-particle event shape variables in 7 TeV pp collisions with detailed comparisons to models.

Findings

Significant deviations between data and Monte Carlo models

Event shape variables vary with charged particle multiplicity and momentum

Results provide constraints for tuning theoretical models

Abstract

The measurement of charged-particle event shape variables is presented in inclusive inelastic pp collisions at a center-of-mass energy of 7 TeV using the ATLAS detector at the LHC. The observables studied are the transverse thrust, thrust minor and transverse sphericity, each defined using the final-state charged particles' momentum components perpendicular to the beam direction. Events with at least six charged particles are selected by a minimum-bias trigger. In addition to the differential distributions, the evolution of each event shape variable as a function of the leading charged particle transverse momentum, charged particle multiplicity and summed transverse momentum is presented. Predictions from several Monte Carlo models show significant deviations from data.