The rather complete data set of hadron yields from central Si + A collisions at the Brookhaven AGS is used to test whether the system at freeze-out is in thermal and hadro-chemical equilibrium. Rapidity and transverse momentum distributions are discussed with regards to the information they provide on hydrodynamic flow.The goal of the ultra-relativistic heavy-ion program at the BNL AGS and CERN SPS is to study highly excited and dense nuclear matter and possibly the transition from hot and dense hadronic matter to deconfined quark-matter with restored chiral symmetry. While future collider experiments will probe a hot quark-gluon plasma with low net baryon density, present fixed target experiments create matter, possibly quark-matter, at very high baryon density and moderate temperature.The present paper is following up on an earlier suggestion by some of us [1], based on the first AGS and SPS data, that a high degree of thermalization is reached and that there is evidence for hydrodynamic expansion of the created fireball. We now use the much larger set of data from central Si + A collisions at the AGS first to discuss quantitatively the 1
ALICE is the heavy-ion experiment at the CERN Large Hadron Collider. The experiment continuously took data during the first physics campaign of the machine from fall 2009 until early 2013, using proton and lead-ion beams. In this paper we describe the running environment and the data handling procedures, and discuss the performance of the ALICE detectors and analysis methods for various physics observables.
In this paper measurements are presented of π ± , K ± , p, andp production at midrapidity (|y| < 0.5), in Pb-Pb collisions at √ s NN = 2.76 TeV as a function of centrality. The measurement covers the transverse-momentum (p T ) range from 100, 200, and 300 MeV/c up to 3, 3, and 4.6 GeV/c for π , K, and p, respectively. The measured p T distributions and yields are compared to expectations based on hydrodynamic, thermal and recombination models. The spectral shapes of central collisions show a stronger radial flow than measured at lower energies, which can be described in hydrodynamic models. In peripheral collisions, the p T distributions are not well reproduced by hydrodynamic models. Ratios of integrated particle yields are found to be nearly independent of centrality. The yield of protons normalized to pions is a factor ∼1.5 lower than the expectation from thermal models.
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