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.
14033897
RELATIVISTIC HEAVY ION PHYSICS: RESULTS FROM AGS TO RHIC
High-energy collisions of heavy ions provide a means to study QCD in a regime of high parton density, and may provide insight into its phme structure. Results from the four experiments at RHIC (BRAHMS, PHENIX, PHOBOS and STAR) are presented, and placed in context with the lower energy data from the AGS and SPS accelerators. The focus is on the insights these measurements provide into the time history of the collision process. Taken together, the data point to the creation of a deconfined state of matter that forms quickly, expands rapidly and freezes out suddenly. With the new RHIC data, systematic data now exists for heavy ion collisions as a function of {radical}s over several orders of magnitude and as a function of impact parameter. These data test the interplay between hard and soft processes in a large-volume system where nucleons are struck multiple times. The data is consistent with creating a deconfined state (jet quenching) that forms quickly (saturation models), expands rapidly (radial and elliptic flow) and freezes out suddenly (single freezeout and blast wave fits). There are also intriguing connections with particle production in elementary systems, which point to the role of the energy available for particle production on the features of the final state. Many in this field are optimistic that the careful understanding of this experimental data may lead t o the theoretical breakthroughs that will connect these complex systems to the fundamental lattice predict ions.
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.
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.
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.
119906527
MEASUREMENT OF THE POLARIZATION PARAMETER IN BACKWARD $pi$$sup +$p ELASTIC SCATTERING AT 1.60, 1.80, 2.11, AND 2.31 GeV/c.
119364085
DOUBLE-HYPERFRAGMENT EVENT PRODUCED BY K$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.)
120606050
Monte Carlo simulation of a gas-sampled hadron calorimeter
Abstract A prototype of the OPAL barrel hadron calorimeter, which is a gas-sampled calorimeter using plastic streamer tubes, was exposed to pions at energies between 1 and 7 GeV. The response of the detector was simulated using the CERN GEANT3 Monte Carlo program. By using the observed high energy muon signals to deduce details of the streamer formation, the Monte Carlo program was able to reproduce the observed calorimeter response. The behavior of the hadron calorimeter when placed behind a lead glass electromagnetic calorimeter was also investigated.
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