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.
53626095
Recent Heavy Ion Results with the ATLAS Detector at the LHC
Results are presented from the ATLAS collaboration from the 2010 LHC heavy ion run, during which nearly 10 inverse microbarns of luminosity were delivered. Soft physics results include charged particle multiplicities and collective ow. The charged particle multiplicity, which tracks initial state entropy production, increases by more than a factor of two relative to the top RHIC energy, with a centrality dependence very similar to that previously measured at RHIC. Measurements of elliptic ow out to large transverse momentum also show similar results to what was measured at RHIC. Extensions of these measurements to higher harmonics have also been made, and can be used to explain structures in the two-particle correlation functions that had long been attributed to jet-medium interactions. New hard probe measurements include single muons, jets and high pT hadrons. Single muons at high momentum are used to extract the yield of W bosons and are found to be consistent within statistical uncertainties with binary collision scaling. Conversely, jets are found to be suppressed in central events by a factor of two relative to peripheral events, with no signicant dependence on the jet energy. Fragmentation functions are also found to be the same in central and peripheral events. Updated asymmetry results conrm previous measurements with increased statistics, and multiple jet cone sizes are presented. Finally, charged hadron spectra have been measured out to 30 GeV, and their centrality dependence relative to peripheral events is similar to that found for jets.
14230369
Systematics of Charged Particle Production in Heavy-Ion Collisions with the PHOBOS Detector at RHIC
The multiplicity of charged particles produced in Au+Au collisions as a function of energy, centrality, rapidity and azimuthal angle has been measured with the PHOBOS detector at RHIC. These results contribute to our understanding of the initial state of heavy ion collisions and provide a means to compare basic features of particle production in nuclear collisions with more elementary 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.
123167372
Direct photons in ATLAS@LHC
The ATLAS detector at the LHC is capable of efficiently separating photons and neutral hadrons based on their shower shapes over a wide range in η, ϕ and ET, either in addition to or instead of isolation cuts. This provides ATLAS with a unique strength for direct photon and γ-jet physics (“tomography”) as well as access to the unique capability to measure non-isolated photons from fragmentation or from the medium. We present a first look at the ATLAS direct photon measurement capabilities in p+p and Pb+Pb collisions at LHC energies over the region |η| < 2.4.
16943370
The Origin of the Difference between Multiplicities in e+e- Annihilation and Heavy Ion Collisions
Multiplicities in e+e- annihilation and relativistic heavy ion collisions show remarkable similarities at high energies. A thermal-statistical model is proposed to explain the differences which occur mainly at low beam energies. Two different calculations are performed, one using an approximate thermodynamic relationship, the other using a full thermal model code. The results are in qualitative agreement, suggesting that the interplay of baryon density and temperature tends to systematically suppress the total multiplicity at lower beam energies.
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.)
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.
120716454
Evidence of muonium formation using thin gold foils in vacuum
117056598
Search for Penetrating Massive Neutral Particles Produced in High Energy Proton Collisions
122067625
Quasielastic charmed-baryon production and exclusive strange-particle production by high-energy neutrinos
Three charmed-baryon candidates produced in the quasielastic reaction ..nu..n..--> mu../sup -/..lambda../sub c//sup +/..--> mu../sup -/..lambda pi../sup +/ were found in an exposure of the Fermilab deuterium-filled 15-ft bubble chamber to a wide-band neutrino beam. We also found that the cross section of the associated-production reaction ..nu..n..--> mu../sup -/..lambda..K/sup +/ is (5.5 +- 1.3 +- 1.1) x 10/sup -40/ cm/sup 2/ for E/sub ..nu../>10 GeV, and is approximately independent of energy. In addition we studied the cross sections of some quasi-two-body associated strange-particle production reactions other than ..mu../sup -/..lambda..K/sup +/.