122715066
Heavy-ion physics with the ATLAS detector at the LHC
The ATLAS experiment will participate in the Heavy Ion program at the Large Hadron Collider (LHC) and will use its large acceptance, high granularity calorimeters, silicon tracking detectors, and muon spectrometers to study hard scattering processes and jet quenching, quarkonia production and suppression, and global observables in Pb+Pb collisions. The longitudinal and fine transverse segmentation of the ATLAS electromagnetic calorimeter gives ATLAS unique capabilities for measuring complete jets and photons. Brookhaven National Laboratory, Columbia University, Iowa State University, and Stony Brook University propose a focused program to take advantage of ATLAS’s strengths to study the physics of high-energy parton interactions with the quark-gluon plasma (QGP), the physics of Debye screening of Q-Q̄ states in the QGP, and the physics of initial particle production and thermalization to characterize the properties of the QGP created in heavy ion collisions at the LHC. The proposed program can be accomplished for modest cost, will provide substantial physics impact and will have a positive impact on the physics program at the Relativistic Heavy Ion Collider (RHIC) due to the strong involvement of the proposing institutions in the RHIC program. Participation of US groups will strengthen the existing (and growing) ATLAS heavy ion program by bringing physics and analysis expertise developed at RHIC and will allow the US Nuclear Physics program to participate in an experiment that will have subtantial physics impact on the heavy ion community.
103715436
Entropy Production at High Energy and mu(B)
The systematics of bulk entropy production in experimental data on Ai-A, p + y and e{sup +}e{sup -} interactions at high energies and large {mu}{sub B} is discussed. It is proposed that scenarios with very early thermalization, such as Landau's hydrodynamical model, capture several essential features of the experimental results. It is also pointed out that the dynamics of systems which reach the hydrodynamic regime give similar multiplicities and angular distributions as those calculated in weak-coupling approximations (e.g. pQCD) over a wide range of beam energies. Finally, it is shown that the dynamics of baryon stopping are relevant to the physics of total entropy production, explaining why A+A and e{sup +}e{sup -} multiplicities are different at low beam energies.
118405036
Quantitative and Conceptual Considerations for Extracting the Knudsen Number in Heavy Ion Collisions
In this article, we examine the methodology for extracting the Knudsen number (K) and the ratio of shear viscosity to entropy density ({eta}/s) developed by Drescher et al. [1]. The final result for {eta}/s turns out to be quite sensitive to Glauber parameters, particularly the parameter x, which controls the balance between N{sub part} and N{sub coll}. We also explore how alternative formulations of the functional relation between the elliptic flow and Knudsen number (K={lambda}/R{sup -}) impacts the physics conclusions, based on Pade approximants. Finally, we extend the calculation to include a limiting minimum value on the mean free path proportional to the DeBroglie wavelength. These results emphasize the importance of clarifying the initial state used in different calculations as well as the ambiguities inherent in using a transport approach in a strongly coupled regime.
53418415
Bulk Dynamics in Heavy Ion Collisions
The features of heavy ion collisions that suggest the relevance of collective dynamics, as opposed to mere superpositions of nucleon-nucleon or even parton-parton collisions, are reviewed. The surprise of these studies is that bulk observables are far simpler than typical dynamical models of nucleus-nucleus collisions would imply. These features are shown to have a natural interpretation in terms of statistical-hydrodynamical models. The relevance of hydrodynamics to heavy ion collisions, coupled with the various similarities of the heavy ion data with that of more elementary collisions, raises very basic questions about its relevance to smaller systems.
1646349
Heavy ion physics at the LHC with the ATLAS detector
The ATLAS detector at CERN will provide a high-resolution longitudinally segmented calorimeter and precision tracking for the upcoming study of heavy ion collisions at the LHC ( GeV). The calorimeter covers |η| < 5 with both electromagnetic and hadronic sections, while the inner detector spectrometer covers |η| < 2.5. ATLAS will study a full range of observables necessary to characterize the hot and dense matter formed at the LHC. Global measurements (particle multiplicities, collective flow) will provide access into its thermodynamic and hydrodynamic properties. Measuring complete jets out to 100's of GeV will allow detailed studies of energy loss and its effect on jets. Quarkonia will provide a handle on deconfinement mechanisms. ATLAS will also study the structure of the nucleon and nucleus using forward physics probes and ultraperipheral collisions, both enabled by segmented zero degree calorimeters.
14828282
Universal behavior of charged particle production in heavy ion collisions at RHIC energies
The PHOBOS experiment at RHIC has measured the multiplicity of primary charged particles as a function of centrality and pseudorapidity in Au+Au collisions at √SNN = 19.6, 130 and 200 GeV. Two kinds of universal behavior are observed in charged particle production in heavy ion collisions. The first is that forward particle production, over a range of energies, follows a universal limiting curve with a non-trivial centrality dependence. The second arises from comparisons with pp/pp and e+e− data. 〈Nch〉/〈Npart/2〉 in nuclear collisions at high energy scales with √s in a similar way as Nch in e+e− collisions and has a very weak centrality dependence. This feature may be related to a reduction in the leading particle effect due to the multiple collisions suffered per participant in heavy ion collisions.
119364085
DOUBLE-HYPERFRAGMENT EVENT PRODUCED BY K$sup -$ INTERACTION AT 2.3 Bev/c IN NUCLEAR EMULSION
An event is shown that consists of two hyperfragments and a meson (K/sup +) coming from a single interaction star found in a nuclear emulsion stack exposed to a meson (K/sup -/) beam at 2.3 and 2.5 Bev/c. Unique identification of the hyperfragments is impossible, but the binding energy favors LAMBDA H/sup 4/ or LAMBDA He/sup 4/. The nature of the production mechanism cannot be determined on the basis of the iniormation available in this single event. (C.E.S.)
119906527
MEASUREMENT OF THE POLARIZATION PARAMETER IN BACKWARD $pi$$sup +$p ELASTIC SCATTERING AT 1.60, 1.80, 2.11, AND 2.31 GeV/c.
122598679
Measurement of the polarization parameter in K$sup +$p elastic scattering
Full angular distributions of the polarization parameter in elastic ${K}^{+}p$ scattering at 1.37, 1.45, 1.60, 1.71, 1.80, 1.89, 2.11, and 2.31 GeV/c are presented. These data were obtained in an experiment at the Zero Gradient Synchrotron using a polarized proton target with arrays of scintillation and \ifmmode \check{C}\else \v{C}\fi{}erenkov counters to detect the scattered particles.
122557716
Measurement of the polarization parameter in K+p elastic scattering at 1.60, 1.80, 2.11 and 2.31 GeV/c
Abstract The polarization parameter for K+p elastic scattering has been measured at 1.60, 1.80, 2.11 and 3.31 GeV/c incident momenta over the entire angular range with an emphasis on the backward region. The results in the extreme backward region appear to be small and consistent with zero.
117056598
Search for Penetrating Massive Neutral Particles Produced in High Energy Proton Collisions