Ultrarelativistic nucleus-nucleus collisions and the quark-gluon plasma

We present an overview of selected aspects of ultrarelativistic nucleus-nucleus collisions, a research program devoted to the study of strongly interacting matter at high energy densities and in particular to the characterization of the quark-gluon plasma (QGP). The basic features of the phase diagram of nuclear matter, as currently understood theoretically, are discussed. The experimental program, carried out over a broad energy domain at various accelerators, is briefly reviewed, with an emphasis on the global characterization of nucleus-nucleus collisions. Two particular aspects are treated in more detail: i) the application of statistical models to a phenomenological description of particle production and the information it provides on the phase diagram; ii) the production of hadrons carrying charm quarks as messengers from the QGP phase.Comment: Based on lectures given by P.Braun-Munzinger at the VIII Hispalensis International Summer School, Oromana (Seville, Spain), June 9-21, 2003 32 pages, 20 figures. A clickable list of references available at http://www-linux.gsi.de/~andronic/qgp/qgp.htm

Strange Particle Production in p+p, p+Pb and Pb+Pb Interactions from NA49

Recent NA49 results on Lambda, Antilambda, Xi- and Antixi+ production in minimum bias p+p and centrality selected p+Pb collisions at 158 GeV/c, and the results on Lambda, Antilambda, K+ and K- production in central Pb+Pb collisions at 40, 80 and 158 A GeV are discussed and compared with other available data. By comparing the energy dependence of Lambda and Antilambda production at mid-rapidity a striking similarity is observed between p+p and A+A data. This is also seen in the energy dependence of the Lambda/pi ratio. K+/pi at mid-rapidity is affected in a similar way, due to the associated production of K+ together with Lambda particles. The observed yields increase faster than the number of wounded nucleons when comparing p+Pb to p+p. As already observed in A+A collisions, the increase is larger for multistrange than for strange baryons and for baryons than for anti-baryons.Comment: 8 pages, 10 figures, To appear in proceedings of Strange Quark in Matter 2001-A Flavourspace Odyssey, Frankfurt am Main, Germany, 24-29. Sept. 200

Directed flow of neutral strange particles at AGS

Directed flow of neutral strange particles in heavy ion collisions at AGS is studied in the ART transport model. Using a lambda mean-field potential which is 2/3 of that for a nucleon as predicted by the constituent quark model, lambdas are found to flow with protons but with a smaller flow parameter as observed in experiments. For kaons, their repulsive potential, which is calculated from the impulse approximation using the measured kaon-nucleon scattering length, leads to a smaller anti-flow than that shown in the preliminary E895 data. Implications of this discrepancy are discussed.Comment: 6 pages, 2 figure

System-size dependence

The final state in The final state in heavy-ion collisions has a higher degree of strangeness saturation than the one produced in collisions between elementary particles like p-p or p-$\bar{p}$. A systematic analysis of this phenomenon is made for C-C, Si-Si and Pb-Pb collisions at the CERN SPS collider and for $Au-Au$ collisions at RHIC and at AGS energies. Strangeness saturation is shown to increase smoothly with the number of participants at AGS, CERN and RHIC energies.Comment: 5 pages, 5 figures, presented at SQM2003 conferenc

Strangeness Report

The paper provides a short report on strangeness production in ultrarelativistic nucleus-nucleus collision, with the main stress on strange particle abundances.Comment: Proceedings of Quark Matter 200

Laying the groundwork at the AGS: Recent results from experiment E895

The E895 Collaboration at the Brookhaven AGS has performed a systematic investigation of Au+Au collisions at 2-8 AGeV, using a large-acceptance Time Projection Chamber. In addition to extensive measurements of particle flow, spectra, two-particle interferometry, and strangeness production, we have performed novel hybrid analyses, including azimuthally-sensitive pion HBT, extraction of the six-dimensional pion phasespace density, and a first measurement of the Lambda-proton correlation function.Comment: Presented at Quark Matter 2001, 8 pages, 5 figure

Lambda production in central Pb+Pb collisions at CERN-SPS energies

In this paper we present recent results from the NA49 experiment for $\Lambda$ and $\bar{\Lambda}$ hyperons produced in central Pb+Pb collisions at 40, 80 and 158 A$\cdot$GeV. Transverse mass spectra and rapidity distributions for $\Lambda$ are shown for all three energies. The shape of the rapidity distribution becomes flatter with increasing beam energy. The multiplicities at mid-rapidity as well as the total yields are studied as a function of collision energy including AGS measurements. The ratio $\Lambda/\pi$ at mid-rapidity and in 4$\pi$ has a maximum around 40 A$\cdot$GeV. In addition, $\bar{\Lambda}$ rapidity distributions have been measured at 40 and 80 A$\cdot$GeV, which allows to study the $\bar{\Lambda}$/$\Lambda$ ratio.Comment: SQM proceedings. J. Phys. G: Nucl. Part. Phys.: submitte