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

Confronting fluctuations of conserved charges in central nuclear collisions at the LHC with predictions from Lattice QCD

We construct net baryon number and strangeness susceptibilities as well as correlations between electric charge and strangeness from experimental data of the ALICE Collaboration at the CERN LHC. The data were taken in Pb-Pb collisions at $\sqrt{s_{NN}}$=2.76 TeV. The resulting fluctuations and correlations are consistent with Lattice QCD results at the chiral crossover pseudocritical temperature $T_c\simeq 155$ MeV. This agreement lends strong support to the assumption that the fireball created in these collisions is of thermal origin and exhibits characteristic properties expected in QCD at the transition from the quark gluon plasma to the hadronic phase. The volume of the fireball for one unit of rapidity at $T_c$ is found to exceed 4000 fm$^3$. A detailed discussion on uncertainties in the temperature and volume of the fireball is presented. The results are linked to pion interferometry measurements and predictions from percolation theory.Comment: 7 pages, 4 figures Accepted for publication in PL

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

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

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

Transverse dynamics of charmed hadrons in ultra-relativistic nuclear collisions

Transverse momentum $p_{\rm T}$ spectra and anisotropic flow distributions are studied for charmonia and charmed hadrons produced in Pb-Pb collisions and measured with the ALICE detector at the CERN Large Hadron Collider (LHC). The investigations are performed within the framework of the Statistical Hadronization Model with the transverse dynamics evaluated using predictions from relativistic viscous hydrodynamics as implemented in the computer codes MUSIC and FluiduM. With this essentially parameter-free approach good agreement is obtained for $p_{\rm T}$ spectra in the range $p_{\rm T} < 10$ GeV/c. The observed wide distribution in $p_{\rm T}$ of anisotropic flow coefficients $v_2$ and $v_3$ for charmonia is also well reproduced, while their magnitude is generally somewhat over predicted. This finding may be connected to a difference in spatial distribution between light and charmed hadrons due to a different diffusion of light and heavy quarks in the hot fireball

Confronting fluctuations of conserved charges in central nuclear collisions at the LHC with predictions from Lattice QCD

We construct net baryon number and strangeness susceptibilities as well as correlations between electric charge, strangeness and baryon number from experimental data at midrapidity of the ALICE Collaborationat CERN. The data were taken in central Pb–Pb collisions at √sNN = 2.76 TeV and cover one unit of rapidity. The resulting fluctuations and correlations are consistent with Lattice QCD results at the chiral crossover pseudocritical temperature Tc ≃ 155 MeV. This agreement lends strong support to the assumption that the fireball created in these collisions is of thermal origin and exhibits characteristic properties expected in QCD at the transition from the quark gluon plasma to the hadronic phase. The volume of the fireball for one unit of rapidity at Tc is found to exceed 3000 fm³. A detailed discussion on uncertainties in the temperature and volume of the fireball is presented. The results are linked to pion interferometry measurements and predictions from percolation theory