Measurement of underlying event characteristics using charged particles in pp collisions at 900 GeV and 7 TeV with the ATLAS detector

THE ATLAS COLL. , G. AAD; MARIA TERESA DOVA ET AL.

PHYSICAL REVIEW D

AMER PHYSICAL SOC

Año: 2011 vol. 83 p. 112001 - 112010

1550-7998

Measurements of charged particle distributions, sensitive to the underlying event, have been per- formed with the ATLAS detector at the LHC. The measurements are based on data collected using a minimum-bias trigger to select proton?proton collisions at center-of-mass energies of 900 GeV and 7 TeV. The ?underlying event? is defined as those aspects of a hadronic interaction attributed not to the hard scattering process, but rather to the accompanying interactions of the rest of the pro- ton. Three regions are defined in azimuthal angle with respect to the highest transverse momentum charged particle in the event, such that the region transverse to the dominant momentum-flow is most sensitive to the underlying event. In each of these regions, distributions of the charged par- ticle multiplicity, transverse momentum density, and average pT are measured. The data show generally higher underlying event activity than that predicted by Monte Carlo models tuned to pre-LHC data.