The underlying event in jet events at 7~TeV with the ATLAS experiment

Particle distributions sensitive to the underlying event in calorimeter jet events have been measured with the ATLAS detector at the LHC, based on 37 pb-1 of proton--proton collision data collected at a centre-of-mass energy of 7 TeV during the LHC run in 2010. Charged particle multiplicity, charged and inclusive sum pT densities and mean charged-particle pT in the regions of each event, azimuthally transverse to the hardest jet, are presented as functions of the hardest jet \pt from 20 GeV to 800 GeV. The mean pT value of the charged particles is also presented as a function of their multiplicity. Separate inclusive jet and exclusive dijet event selections, and event-by-event transverse min/max regions, are included in this study for all observables. When compared to the predictions of different Monte Carlo models, the data show sensitivity to the modelling of the underlying event.