We review the main results obtained by the BRAHMS collaboration on the properties of hot and dense hadronic and partonic matter produced in ultrarelativistic heavy ion collisions at RHIC. A particular focus of this paper is to discuss to what extent the results collected so far by BRAHMS, and by the other three experiments at RHIC, can be taken as evidence for the formation of a state of deconfined partonic matter, the so called quark-gluon-plasma (QGP). We also discuss evidence for a possible precursor state to the QGP, i.e. the proposed Color Glass Condensate.

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Data from a number of different experimental measurements have been used to construct caloric curves for five different regions of nuclear mass. These curves are qualitatively similar and exhibit plateaus at the higher excitation energies. The limiting temperatures represented by the plateaus decrease with increasing nuclear mass and are in very good agreement with results of recent calculations employing either a chiral symmetry model or the Gogny interaction. This agreement strongly favors a soft equation of state. Evidence is presented that critical excitation energies and critical temperatures for nuclei can be determined over a large mass range when the mass variations inherent in many caloric curve measurements are taken into account.Comment: In response to referees comments we have improved the discussion of the figures and added a new figure showing the relationship between the effective level density and the excitation energy. The discussion has been reordered and comments are made on recent data which support the hypothesis of a mass dependence of caloric curve

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The symmetry energy of nuclear matter is a fundamental ingredient in the investigation of exotic nuclei, heavy-ion collisions, and astrophysical phenomena. New data from heavy-ion collisions can be used to extract the free symmetry energy and the internal symmetry energy at subsaturation densities and temperatures below 10 MeV. Conventional theoretical calculations of the symmetry energy based on mean-field approaches fail to give the correct low-temperature, low-density limit that is governed by correlations, in particular, by the appearance of bound states. A recently developed quantum-statistical approach that takes the formation of clusters into account predicts symmetry energies that are in very good agreement with the experimental data. A consistent description of the symmetry energy is given that joins the correct low-density limit with quasiparticle approaches valid near the saturation density.

From experimental observations of limiting temperatures in heavy ion collisions we derive Tc, the critical temperature of infinite nuclear matter. The critical temperature is 16.6 ± 0.86 MeV. Theoretical model correlations between Tc, the compressibility modulus, K the effective mass, m * and the saturation density, ρs, are exploited to derive the quantity (K/m * )s . This quantity together with calculations employing Skyrme and Gogny interactions indicates a nuclear matter incompressibility in moderately excited nuclei that is in excellent agreement with the value determined from Giant Monopole Resonance data. This technique of extraction of K may prove particularly useful in investigations of very neutron rich systems using radioactive beams.PACS numbers: 24.10.i,25.70.Gh Improved knowledge of the nuclear equation of state and a coherent picture of the relationship between the properties of finite nuclei and bulk nuclear matter remains a key requirement in both nuclear physics and astrophysics. It is key, for example, to understanding nuclear structure, heavy ion collisions, supernova explosions and neutron star properties [1,2,3]. Significant effort has been devoted to the development of microscopic theoretical models which can provide reliable mathematical formulations of this equation of state [4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20]. Such calculations are usually specified for symmetric nuclear matter, a hypothetical system of equal numbers of neutrons and (uncharged) protons interacting through nuclear forces. Driven by the astrophysical problems and more recent laboratory excursions into the region of more exotic nuclei, the dependence of the equation of state on neutronproton asymmetry has also become a subject of significant interest. [21,22,23]. In this letter we employ data from experimental measurements of caloric curves in nuclear collisions, together with systematic trends and correlations derived from a number of theoretical investigations of nuclear matter, to derive the critical temperature and incompressibility of symmetric nuclear matter. The techniques employed offer a natural method to extend such investigations to more asymmetric systems.In a recent paper measurements of nuclear specific heats from a large number of experiments were employed to construct caloric curves for five different regions of nuclear mass [24]. Within experimental uncertainties each of these caloric curves exhibits a plateau region at higher excitation energy, i.e., a "limiting temperature" is reached. In Figure 1 these limiting temperatures from reference [24] are presented as a function of mass. As previously noted, they are observed to decrease with increasing mass. This decrease with increasing mass has long been predicted as resulting from Coulomb Instabilities of expanded and heated nuclei [25,26,27,28,29,30,31,32,33,34,35].The results employed in reference [24] were based upon temperature determinations derived from double isotope yield ratios and from slope measurements of particle spectra. More rece...

We report on a study of the transverse momentum dependence of nuclear modification factors R dAu for charged hadrons produced in deuteron + gold collisions at √ sNN = 200 GeV, as a function of collision centrality and of the pseudorapidity (η = 0, 1, 2.2, 3.2) of the produced hadrons. We find a significant and systematic decrease of R dAu with increasing rapidity. The mid-rapidity enhancement and the forward rapidity suppression are more pronounced in central collisions relative to peripheral collisions. These results are relevant to the study of the possible onset of gluon saturation at energies reached at BNL RHIC.

We discuss experimental evidence for a nuclear phase transition driven by the different concentration of neutrons to protons. Different ratios of the neutron to proton concentrations lead to different critical points for the phase transition. This is analogous to the phase transitions occurring in 4 He-3 He liquid mixtures. We present experimental results which reveal the N/A (or Z/A) dependence of the phase transition and discuss possible implications of these observations in terms of the Landau Free Energy description of critical phenomena.