Heavy-ion physics with the ATLAS detector
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ELEMENTARY PARTICLES AND FIELDS Experiment
Heavy-Ion Physics with the ATLAS Detector* V. N. Pozdnyakov** (on behalf of the ATLAS Collaboration) Joint Institute for Nuclear Research, Dubna, Moscow oblast, 141980 Russia Received March 26, 2008
√ Abstract—The CERN LHC collider will operate with lead ions at s of 5.5 TeV/nucleon. The ATLAS detector, designed to study high-pT physics in the pp mode of the LHC, has the potential to study ultrarelativistic heavy-ion collisions in a full range of observables characterized extremely dense matter and the formation of a quark–gluon plasma. The ATLAS physics program includes global event measurements (particle multiplicities, transverse momentum), suppression of heavy-quarkonia production, jet quenching, and a study of ultraperipheral collisions. PACS numbers: 13.75.Cs, 25.20.-x, 25.75.-q DOI: 10.1134/S1063778808090056
1. INTRODUCTION Ultrarelativistic heavy-ion central collisions at the LHC will create hot and dense matter with an enormous number of virtual deconfined partons. This new phase of QCD matter, called quark–gluon plasma (QGP), is characterized by deconfined partons and by a partial restoration of chiral symmetry. The study of produced jets, direct photons, and heavy quarks will probe the earliest stage of collisions [1]. Modification of these processes compared to proton–proton collisions will allow one to learn about QCD in a dense medium [2]. The analysis of particle multiplicities, transverse momentum, and monojets intends to study the parton structure of the nucleus. Gluon radiation by partons moving through dense matter, often referred to as jet quenching [3], should reflect the properties of produced jets. The ATLAS setup [4] includes different elements: inner detector for precise measurements of charged particles (covering |η| < 2.5) located inside a 2-T solenoid magnet, finely granulated and longitudinal segmented electromagnetic (|η| < 3) and hadronic (|η| < 4.9) calorimeters, and stand-alone muon spectrometer in a toroidal field. Quite an important detector for heavy-ion physic studies is the Zero Degree Calorimeter [5] intended for detection of forward neutrons and as an estimator of the event “centrality.” A view of the ATLAS setup is shown in Fig. 1. The ∗ **
The text was submitted by the author in English. E-mail: [email protected]
ATLAS detector is well suited to address many theoretical questions via precise experimental measurements using tools developed in the context of RHIC studies [6].
2. OBSERVABLES The heavy ion simulation was done with the HIJING-1.38 event generator [7] and then the GEANT simulation package [8]. It is worthwhile to mention that the simulation probably overestimates the detector occupancy since extrapolated RHIC data [9] show that particle densities should be a factor of 2–3 lower compared to the HIJING expectation of around 3000 particles per unit of pseudorapidity for central PbPb interactions. So we realized a “pessimistic” scenario, and values of detector occupancies and reconstruction efficiency given below are to b
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