The Beam Energy Scan (BES) program at RHIC was launched with the specific aim to explore the QCD (Quantum Chromodynamics) Phase Diagram. Particular emphasis was given to the search for phase ...boundaries and the location of the Critical Point (CP). The first run with AuAu collisions at 7.7, 11.5, and 39 GeV took place in 2010, and the next one, with energies of 18 and 27 GeV, will start in a few months. The results of the first stage of the BES program obtained by the STAR (Solenoidal Tracker at RHIC) experiment are presented and discussed, as well as plans for the future of the program.
The analysis of the statistical and dynamical fluctuations in nucleus-nucleus collisions on an event-by-event basis strongly relies on a comparison with specially constructed artificial events where ...statistical fluctuations and kiuematical correlations are under control. In this paper, we present a novel, analytical method of constructing reference events based on independent emission, modified by the energy/momentum constraint, which can lead to a better understanding of the nature of the observed final-state fluctuations. This approach can be easily used in the analysis of other topics in the heavy ion field (e.g. flow, HBT etc.) allowing more precise measurements.
Standard jet-finding techniques used in elementary particle collisions have not been successful in the high track density of heavy-ion collisions. This paper describes a modified cone-type ...jet-finding algorithm developed for the complex environment of heavy-ion collisions. The primary modification to the algorithm is the evaluation and subtraction of the large background energy, arising from uncorrelated soft hadrons, in each collision. A detailed analysis of the background energy and its event-by-event fluctuations has been performed on simulated data, and a method developed to estimate the background energy inside the jet cone from the measured energy outside the cone on an event-by-event basis. The algorithm has been tested using Monte Carlo simulations of Pb+Pb collisions at {radical}s=5.5 TeV for the ALICE detector at the LHC. The algorithm can reconstruct jets with a transverse energy of 50 GeV and above with an energy resolution of {approx}30%.
Novel transverse-momentum technique is used to analyse charged-particle exclusive data for collective motion in the Ar+KCl reaction at 1.8 GeV/nucl. Previous analysis of this reaction, employing the ...standard sphericity tensor, revealed no significant effect. In the present analysis, collective effects are observed, and they are substantially stronger than in the Cugnon cascade model, but weaker than in the hydrodynamical model.
We report a particle source imaging analysis based on two-pion correlations in high multiplicity Au+Au collisions at beam energies between 2A and 8A GeV. We apply the imaging technique introduced by ...Brown and Danielewicz, which allows a model-independent extraction of source functions with useful accuracy out to relative pion separations of about 20 fm. The extracted source functions have Gaussian shapes. Values of source functions at zero separation are almost constant across the energy range under study. Imaging results are found to be consistent with conventional source parameters obtained from a multidimensional Hanburg-Brown-Twiss analysis.
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