Systematic measurements of identified particle spectra inpp,d+Au, andAu

Abstract

Identified charged-particle spectra of π ± , K ± , p, and p at midrapidity (|y| < 0.1) measured by the dE/dx method in the STAR (solenoidal tracker at the BNL Relativistic Heavy Ion Collider) time projection chamber are reported for pp and d + Au collisions at √ s NN = 200 GeV and for Au + Au collisions at 62.4, 130, and 200 GeV. Average transverse momenta, total particle production, particle yield ratios, strangeness, and baryon production rates are investigated as a function of the collision system and centrality. The transverse momentum spectra are found to be flatter for heavy particles than for light particles in all collision systems; the effect is more prominent for more central collisions. The extracted average transverse momentum of each particle species follows a trend determined by the total charged-particle multiplicity density. The Bjorken energy density estimate is at least several GeV/fm 3 for a formation time less than 1 fm/c. A significantly larger net-baryon density and a stronger increase of the net-baryon density with centrality are found in Au + Au collisions at 62.4 GeV than at the two higher energies. Antibaryon production relative to total particle multiplicity is found to be constant over centrality, but increases with the collision energy. Strangeness production relative to total particle multiplicity is similar at the three measured RHIC energies. Relative strangeness production increases quickly 034909-2 SYSTEMATIC MEASUREMENTS OF IDENTIFIED . . . (2009) with centrality in peripheral Au + Au collisions, to a value about 50% above the pp value, and remains rather constant in more central collisions. Bulk freeze-out properties are extracted from thermal equilibrium model and hydrodynamics-motivated blast-wave model fits to the data. Resonance decays are found to have little effect on the extracted kinetic freeze-out parameters because of the transverse momentum range of our measurements. The extracted chemical freeze-out temperature is constant, independent of collision system or centrality; its value is close to the predicted phase-transition temperature, suggesting that chemical freeze-out happens in the vicinity of hadronization and the chemical freeze-out temperature is universal despite the vastly different initial conditions in the collision systems. The extracted kinetic freeze-out temperature, while similar to the chemical freeze-out temperature in pp, d + Au, and peripheral Au + Au collisions, drops significantly with centrality in Au + Au collisions, whereas the extracted transverse radial flow velocity increases rapidly with centrality. There appears to be a prolonged period of particle elastic scatterings from chemical to kinetic freeze-out in central Au + Au collisions. The bulk properties extracted at chemical and kinetic freeze-out are observed to evolve smoothly over the measured energy range, collision systems, and collision centralities. PHYSICAL REVIEW C 79, 034909

Measurement of transverse energy at midrapidity in Pb-Pb collisions atsNN=2.76TeV

“…Data from RHIC have been scaled by a factor of 2.7 for comparison of the shapes. The factor of 2.7 is approximately the ratio of p T dN ch /dη at the LHC [45] to that at RHIC [62,63]. The shapes observed by ALICE and PHENIX are comparable for all N part .…”

Transverse momentum dependence of D-meson production in Pb-Pb collisions at s N N = 2.76 $$ \sqrt{{\mathrm{s}}_{\mathrm{NN}}}=2.76 $$ TeV

“…This effect could be enhanced by hadronisation via recombination, which is predicted in some models to contribute significantly to hadron formation at low and intermediate p T [15]. The momentum distributions of identified light-flavour hadrons at the LHC [67,68] indicate that the radial flow of the medium at LHC energies is about 10% higher than at RHIC [69]. However, this stronger radial flow does not necessarily give rise to a more pronounced bump-like structure in the R AA at low p T with increasing collision energy, because its effect can be counterbalanced by the different shape of the momentum spectra in pp collisions at different √ s [70,71].…”

Production of light nuclei and anti-nuclei inppand Pb-Pb collisions at energies available at the CERN Large Hadron Collider

“…p/p and the p/π ratios hardly vary with centrality [41,52] showing that T chem and μ B do not vary with centrality in high energy collisions. In a coalescence approach, the centrality independence disfavors implementations in which the nuclei production is proportional to the absolute proton multiplicity [53] rather than the particle density.…”