Abstract
Jets are identified and their properties studied in center-of-mass energy sqrt(s) = 7 TeV proton-proton collisions at the Large Hadron Collider using charged particles measured by the ATLAS inner detector. Events are selected using a minimum bias trigger, allowing jets at very low transverse momentum to be observed and their characteristics in the transition to high-momentum fully perturbative jets to be studied. Jets are reconstructed using the anti-kt algorithm applied to charged particles with two radius parameter choices, 0.4 and 0.6. An inclusive charged jet transverse momentum cross section measurement from 4 GeV to 100 GeV is shown for four ranges in rapidity extending to 1.9 and corrected to charged particle-level truth jets. The transverse momenta and longitudinal momentum fractions of charged particles within jets are measured, along with the charged particle multiplicity and the particle density as a function of radial distance from the jet axis. Comparison of the data with the theoretical models implemented in existing tunings of Monte Carlo event generators indicates reasonable overall agreement between data and Monte Carlo. These comparisons are sensitive to Monte Carlo parton showering, hadronization, and soft physics models.
Highlights
Quantum chromodynamics (QCD) [1,2] provides an excellent description of the kinematic distribution of high transverse momentum jets in proton-proton collisions, but does not give straightforward predictions for the properties of particles within these jets or for the properties of lowmomentum jets
The corrections used in this analysis, from detector-level track jets to truth-level charged particle jets, are derived from a Monte Carlo (MC) simulated sample using the PYTHIA 6.421 event generator program [18] with the ATLAS AMBT1 tune, whose parameters are chosen based on single-track distributions in ATLAS minimum bias data [3]
In order to select goodquality tracks emerging from the primary vertex while maintaining a high efficiency, each track is required to have: (i) transverse momentum pT > 300 MeV; (ii) pseudorapidity jj < 2:5; (iii) transverse impact parameter with respect to the primary vertex jd0j < 1:5 mm (0.2 mm) for tracks with pT less than 10 GeV; (iv) longitudinal impact parameter with respect to the primary vertex z0 satisfying jz0 sinj < 1:5 mm; (v) if a signal is expected in the innermost pixel detector layer, such a hit is required, with one pixel hit in any layer required otherwise; (vi) at least 6 silicon microstrip detector (SCT) hits
Summary
Quantum chromodynamics (QCD) [1,2] provides an excellent description of the kinematic distribution of high transverse momentum jets in proton-proton collisions, but does not give straightforward predictions for the properties of particles within these jets or for the properties of lowmomentum jets. In this work the properties of low-momentum jets are mdaetaasautrecdenftreorm-ofc-hmaragsesdenpearrgtiyclpe ffistffira1⁄4ck7s in the ATLAS 2010 TeV These properties will be compared to a range of Monte Carlo tunes derived from previously measured data, allowing the study of the transition between the MC generators’ separatelyimplemented models of soft strong interactions and perturbative QCD.
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