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.
We present the first excitation function of pi(-) intensity interferometry at Alternating Gradient Synchrotron (AGS) energies (2-8 A GeV). The sensitivity of the multidimensional correlation ...functions to the geometry and dynamics of the pion-emitting system provides a stringent test of transport models of heavy ion collisions. Detailed comparisons with a realistic transport model, both with and without an explicit nuclear mean field, suggest that the beam energy evolution in the reaction dynamics is different in the model than in the data. A significantly increased pi(-) emission time scale, which has been suggested as a signal of the onset of the transition to quark-gluon plasma, is not observed.
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.
The design of a time projection chamber (TPC) detector with complete pad coverage is presented. The TPC allows the measurements of high multiplicity ( approximately 200 tracks) relativistic ...nucleus-nucleus collisions initiated with the heaviest, most energetic projectiles available at the LBL (Lawrence Berkeley Laboratory) BEVALAC accelerator facility. The front-end electronics, composed of over 15000 time sampling channels, is located on the chamber. The highly integrated, custom-designed electronics and the VME-based data acquisition system are described.< >
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