Hadronic event shapes have been measured in proton-proton collisions at sqrt(s)=7 TeV, with a data sample collected with the CMS detector at the LHC. The sample corresponds to an integrated luminosity of 3.2 inverse picobarns. Event-shape distributions, corrected for detector response, are compared with five models of QCD multijet production.
Distribution of the logarithm of the central transverse thrust for events with jet transverse momentum > 30 GeV, jet |pseudorapidity| < 1.3 and leading the jet transverse momentum from 90 to 125 GeV/c,.
Distribution of the logarithm of the central thrust minor for events with jet transverse momentum > 30 GeV, jet |pseudorapidity| < 1.3 and leading the jet transverse momentum from 90 to 125 GeV/c,.
Distribution of the logarithm of the central transverse thrust for events with jet transverse momentum > 30 GeV, jet |pseudorapidity| < 1.3 and leading the jet transverse momentum from 125 to 200 GeV/c,.
Measurements of dijet azimuthal decorrelations in pp collisions at sqrt(s) = 7 TeV using the CMS detector at the CERN LHC are presented. The analysis is based on an inclusive dijet event sample corresponding to an integrated luminosity of 2.9 inverse picobarns. The results are compared to predictions from perturbative QCD calculations and various Monte Carlo event generators. The dijet azimuthal distributions are found to be sensitive to initial-state gluon radiation.
Normalized Delta_Phi distributions for events with a maximum jet pT between 80 and 110 GeV.
Normalized Delta_Phi distributions for events with a maximum jet pT between 110 and 140 GeV.
Normalized Delta_Phi distributions for events with a maximum jet pT between 140 and 200 GeV.
This Letter reports on a first measurement of the inclusive W+jets cross section in proton-proton collisions at a centre-of-mass energy of 7 TeV at the LHC, with the ATLAS detector. Cross sections, in both the electron and muon decay modes of the W boson, are presented as a function of jet multiplicity and of the transverse momentum of the leading and next-to-leading jets in the event. Measurements are also presented of the ratio of cross sections sigma(W+ \ge n) / sigma(W+ \ge n-1) for inclusive jet multiplicities n=1-4. The results, based on an integrated luminosity of 1.3 pb-1, have been corrected for all known detector effects and are quoted in a limited and well-defined range of jet and lepton kinematics. The measured cross sections are compared to particle-level predictions based on perturbative QCD. Next-to-leading order calculations, studied here for n \le 2, are found in good agreement with the data. Leading-order multiparton event generators, normalized to the NNLO total cross section, describe the data well for all measured jet multiplicities.
The measured cross section times branching ratio for W+jets in the electron channel as a function of corrected jet multiplicity.
The measured cross section times branching ratio for W+jets in the muon channel as a function of corrected jet multiplicity.
The measured cross section ratio for W+jets in the electron channel as a function of corrected jet multiplicity.
Using the ATLAS detector, observations have been made of a centrality-dependent dijet asymmetry in the collisions of lead ions at the Large Hadron Collider. In a sample of lead-lead events with a per-nucleon center of mass energy of 2.76 TeV, selected with a minimum bias trigger, jets are reconstructed in fine-grained, longitudinally-segmented electromagnetic and hadronic calorimeters. The underlying event is measured and subtracted event-by-event, giving estimates of jet transverse energy above the ambient background. The transverse energies of dijets in opposite hemispheres is observed to become systematically more unbalanced with increasing event centrality leading to a large number of events which contain highly asymmetric dijets. This is the first observation of an enhancement of events with such large dijet asymmetries, not observed in proton-proton collisions, and which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.
Asymmetry in the different centrality regions for 2.76 TeV/Nucleon PB-PB collisions.
Asymmetry in 7 TeV P-P collisions.
DeltaPhi distribution in the different centrality regions for 2.76 TeV/Nucleon PB-PB collisions.
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