Chemical Equilibration and the Hadron-QGP Phase Transition

We discuss recent experimental results on hadron multiplicities in ultra-relativistic nuclear collisions. The data for central collisions are in quantitative agreement with predictions of a thermal model assuming full chemical equilibration. It is argued that this provides strong, albeit indirect, evidence for the formation of a partonic phase in the collision prior to hadron production.Comment: Contribution to CRIS2000 conference, to be published in Nucl. Phys.

Physics of Ultra-Relativistic Nuclear Collisions with Heavy Beams at LHC Energy

We discuss current plans for experiments with ultra-relativistic nuclear collisions with heavy beams at LHC energy ($\sqrt{s} = 5.5$ TeV/nucleon pair). Emphasis will be placed on processes which are unique to the LHC program. They include event-by-event interferometry, complete spectroscopy of the $\Upsilon$ resonances, and open charm and open beauty measurements.Comment: 11 pages, 6 figures, Quark Matter 99 conference contribution, Nucl. Phys. A to be publishe

Towards the Quark Gluon Plasma

We discuss recent experimental results in the field of ultra-relativistic nuclear collisions. The emerging ``picture'' is a collectively expanding, initially hot and dense fireball in which strangeness- and low-mass di-lepton pair production are enhanced and J/$\Psi$ production is suppressed compared to expectations from nucleon-nucleon collisions. It is argued that, taken together, these data provide circumstantial evidence that a (at least partly) partonic phase was produced in such collisions.Comment: 8 pages, 5 figures, plenary paper, PANIC99 Conference, Uppsala, Sweden, Nucl. Phys. A (in print

Dynamics of Ultra-Relativistic Nuclear Collisions with Heavy Beams: An Experimental Overview

We review, from an experimental point of view, the current status of ultra-relativistic nuclear collisions with heavy beams.Comment: 16 pages, 9 figure

Laser calibration system for the CERES Time Projection Chamber

A Nd:YAG laser was used to simulate charged particle tracks at known positions in the CERES Time Projection Chamber at the CERN SPS. The system was primarily developed to study the response of the readout electronics and to calibrate the electron drift velocity. Further applications were the determination of the gating grid transparency, the chamber position calibration, and long-term monitoring of drift properties of the gas in the detector.Comment: 28 pages, 26 figures; reference to the TPC preprint update

Energy and Charged Particle Flow in 10.8 A GeV/c Au+Au Collisions

Experimental results and a detailed analysis are presented of the transverse energy and charged particle azimuthal distributions measured by the E877 collaboration for different centralities of Au+Au collisions at a beam momentum of 10.8 A GeV/c. The anisotropy of these distributions is studied with respect to the reaction plane reconstructed on an event-by-event basis using the transverse energy distribution measured by calorimeters. Results are corrected for the reaction plane resolution. For semicentral events we observe directed flow signals of up to ten percent. We observe a stronger anisotropy for slow charged particles. For both the charged particle and transverse energy distributions we observe a small but non zero elliptic anisotropy with the major axis pointing into the reaction plane. Combining the information on transverse energy and charged particle flow we obtain information on the flow of nucleons and pions. The data are compared to event generators and the need to introduce a mean field or nucleon-nucleon potential is discussed.Comment: RevTex, 25 pages, 13 figures included as one Postscript file, submitted to Phys. Rev.

Hotter, Denser, Faster, Smaller...and Nearly-Perfect: What's the matter at RHIC?

The experimental and theoretical status of the ``near perfect fluid'' at RHIC is discussed. While the hydrodynamic paradigm for understanding collisions at RHIC is well-established, there remain many important open questions to address in order to understand its relevance and scope. It is also a crucial issue to understand how the early equilibration is achieved, requiring insight into the active degrees of freedom at early times.Comment: 10 Pages, 13 Figures, submitted to the proceedings of the Second Meeting of the APS Topical Group on Hadronic Physics, Nashville, TN, October 22-24, 200

QCD under extreme conditions

In nucleus-nucleus collisions at relativistic energies a new kind of matter is created, the Quark-Gluon Plasma (QGP). The phase diagram of such matter and the chemical freeze-out points will be presented in connection to the pseudo-critical temperature for the chiral cross over transition. The role of conserved charge fluctuations to give experimental access to the nature of the chiral phase transition will be summarized in terms of the relation to lattice QCD and the current experimental data. The QGP can be characterized as a nearly ideal liquid expanding hydrodynamically and the experimental data allow to extract transport parameters such as the bulk and shear viscosities. The energy loss of partons in the QGP probes the high parton density of the medium. The role of quarkonia and open charm hadrons as a probe of deconfinement and hadronization form the final topic.Comment: Article to appear in a special EPJC Volume in celebration of '50 Years of Quantum Chromodynamics' [arXiv:2212.11107

Physics of Coulomb Corrections in Hanbury-Brown Twiss Interferometry in Ultrarelativistic Heavy Ion Collisions

We discuss the elementary physics of the final state Coulomb interactions in Hanbury-Brown Twiss interferometry, showing -- with explicit comparison to E877 data for $\pi^+\pi^-$ and $\pi^\pm p$ -- that the Coulomb corrections in the pair correlation function can be well understood in terms of simple classical physics. We connect the classical picture with descriptions in terms of Coulomb wave functions, and investigate the influence of the ``central'' Coulomb potential on the pair correlation function.Comment: 11 pages, latex, 4 figures submitted to Nuclear Physics A (Quark Matter 1996 Proceedings