Hadron freeze-out conditions in high energy nuclear collisions

Abstract

Systematic trend of the hadron freeze-out conditions from AGS/SPS to RHIC is discussed. The most interesting results from collisions at RHIC are that the system is indeed approaching net-baryon free and the transverse expansion is much stronger than that from collisions at AGS/SPS energies. In order to understand the trend of the collective velocity, an energy scan between $\sqrt{s_{NN}} = 20 - 200 GeV, is important. In addition, systematic studies on the anisotropy parameter $v_2$ and the transverse momentum distributions of $\phi, \Omega,$ and $J / \psi$ are necessary as they will help in determining whether the collectivity is developed at the partonic stage.Comment: Talk presented at the Quark Matter 2001 conference, 8 pages, 8 figures. To appear in Nucl. Phys.

Hydrodynamic description of spectra at high transverse mass in ultrarelativistic heavy ion collisions

“…This finding is in contradiction with the result presented in [22] that the collective flow is stronger at RHIC. It can, however, be seen in [22] that this is strongly influenced by the proton and antiproton spectra from STAR used in the analysis, which show a much larger inverse slope than the PHENIX results. From the SPS data it is clear that a Gaussian-like profile, which leads to an overprediction of the pion yield at high m T , is excluded.…”

“…Assuming a very large flow velocity of β T ≈ 0.55 as in [5] and [8], a temperature of T kin ≈ 90 MeV would be required, in line with the results of [8], but contradicting the values quoted in [5], however, no good fit can be obtained. The present results for the best fit appear to agree with the values given in [22], which are also derived from SPS data.…”

FEMTOSCOPY IN RELATIVISTIC HEAVY ION COLLISIONS: Two Decades of Progress

“…72). Blast-wave fits to spectra (183) indicate that freeze-out flow and temperature vary significantly with √ s NN for √ s NN 10 GeV. The overall approximate √ s NN -independence of the α i parameters may reflect the fact that significantly changing the slope of R i (m T ) requires very large changes in flow and temperature; on the other hand, it could be that the compensating effects of smaller (larger) homogeneity lengths generated by larger flow (temperature) cancel almost exactly in nature.…”

Extraction of Kinetic Freeze-out Properties and Effect of Resonance Decays

“…Particle yield ratios are used to extract chemical freezeout parameters using local equilibrium models [ 9,10]. The chemical freeze-out temperature (T ch ) is independent of centrality and collision energy.…”