ATLAS explores new frontiers with high-p_T jet measurements

The ATLAS collaboration has announced its latest cross-section measurements of inclusive jet and dijet production, which involve final states containing at least one or two jets, respectively. Each jet is the result of a parton (quark or gluon) that emits radiation through the strong force, creating a collimated spray of hadrons.

These high-p_T jet measurements confront QCD, the theory of the strong force, in a large and previously unexplored kinematic region in jet transverse-momentum and dijet invariant-mass. The measurements constitute one of the most stringent tests of QCD ever performed. They probe predictions of perturbative QCD, constrain the density of partons within the proton and are sensitive to new physics scenarios, such as quark compositeness, which may become apparent at very short distance scales.

The analysis uses the full data sample collected in LHC proton–proton collisions at 7 TeV during 2010, corresponding to an integrated luminosity of 37 pb^–1. The results extend far beyond the kinematic reach achieved at the Tevatron, as do recent results from CMS (CMS collaboration 2011). The ATLAS results extend to 1.5 TeV in jet transverse-momentum (as in figure 1) and to 4.1 TeV in dijet invariant-mass. These jet measurements also provide unprecedented coverage out to forward rapidities of ΙyΙ < 4.4. Next-to-leading order perturbative QCD predictions are found to be in good agreement with the measured data across 10 orders of magnitude in cross-section (figure 2).

The jet cross-section measurements have been corrected for detector effects, and the analysis exploits a greatly improved understanding of the detector performance. The dominant source of systematic uncertainty is in the calibration of the jet energy scale, which has been determined to within 2.5% for central jets with p_T above 60 GeV.

A publication is currently in preparation. Work is on-going to reduce the systematic uncertainties further and the collaboration will extend the kinematic reach of these exciting high-p_T jet measurements with much larger datasets in 2011–2012.