Cited by 10.7kOpen Access
Argonne National Laboratory
Publishes on Particle physics theoretical and experimental studies, High-Energy Particle Collisions Research, Particle Detector Development and Performance. 266 papers and 34.8k citations.
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52 páginas, 10 figuras, 18 tablas.-- This article is distributed under the terms of the Creative \nCommons Attribution Noncommercial License.-- et al. (The ATLAS Collaboration).
By 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 transverse energies of dijets in opposite hemispheres are 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, which may point to an interpretation in terms of strong jet energy loss in a hot, dense medium.
A detailed study is presented of the expected performance of the ATLAS detector. The reconstruction of tracks, leptons, photons, missing energy and jets is investigated, together with the performance of b-tagging and the trigger. The physics potential for a variety of interesting physics processes, within the Standard Model and beyond, is examined. The study comprises a series of notes based on simulations of the detector and physics processes, with particular emphasis given to the data expected from the first years of operation of the LHC at CERN.
A combined search for the Standard Model Higgs boson with the ATLAS experiment at the LHC using datasets corresponding to integrated luminosities from 1.04 fb -1 to 4.9 fb -1 of pp collisions collected at s = 7 TeV is presented. The Higgs boson mass ranges 112.9-115.5 GeV, 131-238 GeV and 251-466 GeV are excluded at the 95% confidence level (CL), while the range 124-519 GeV is expected to be excluded in the absence of a signal. An excess of events is observed around m H 126 GeV with a local significance of 3.5 standard deviations ( ). The local significances of H , H Z Z ( * ) + -+ - and H W W ( * ) + -, the three most sensitive channels in this mass range, are 2.8 , 2.1 and 1.4 , respectively. The global probability for the background to produce such a fluctuation anywhere in the explored Higgs boson mass range 110-600 GeV is estimated to be 1.4% or, equivalently, 2.2 .