abstract

We present the results from the BRAHMS experiment at the Relativistic Heavy Ion Collider (RHIC) for the \(^{197}\)Au\( + ^{197}\)Au reaction at \(\sqrt {s_{NN}}\) = 130 GeV and \(\sqrt {s_{NN}}\) = 200 GeV. The main focus is here on the determination of the pseudorapidity distribution of charged particles produced in the reaction as a function of pseudorapidity and centrality and on the measurement of the anti-proton to proton ratio as a function of rapidity. Our measurements show that up to 3860 and 4630 charged particles are produced in the top 5% central collisions and that the number of produced particles per participating nucleon pair exceeds values from \(p + p\) collisions by about 40% and 50% for \(\sqrt {s_{NN}}\) = 130 GeV and \(\sqrt {s_{NN}}\) = 200 GeV, respectively. The \(N(\overline {p})\)/\(N(p)\) ratio at mid-rapidity is found to be 0.64 \(\pm \) 0.06 for the lower, and around 0.75 for the top RHIC energy. These values are the highest observed so far in nucleus–nucleus reaction and show a tendency for matter and antimatter to balance at mid-rapidity as the bombarding energy increases, they also indicate that the net-bayron free mid-rapidity plateau (Bjorken limit) is not reached at this RHIC energies. It is also shown that current models are not able to consistently describe the particle multiplicities and the baryonic ratios.

abstract

Selected data from the first two running periods of the PHENIX detector at the Relativistic Heavy Ion Collider are presented and discussed. These results emphasize charged particle multiplicity as a function of centrality, suppression of hadron production at high transverse momentum, and an estimate of open charm production from single electron spectra.

abstract

The PHOBOS detector, one of the two small experiments at RHIC, focuses on measurements of charged particle multiplicity over almost the full phase space and identified particles near mid-rapidity. Results will be presented from the early RHIC gold–gold runs at nucleon–nucleon center of mass energies of 56 and 130 GeV as well as the recently concluded run at the full RHIC energy of 200 GeV.

abstract

The STAR detector at RHIC has made a wide variety of measurements from \(\sqrt {{s}_{_{{NN}}}} = 130\) GeV Au + Au collisions. The overview presented here focuses on hadron production. The yields and spectra of various hadronic species have been measured giving information on the properties and evolution of the fireball created in the collision.

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The methods of centrality measurements in the PHOBOS experiment are presented. The precision and uncertainties in centrality determination are discussed.

abstract

Experimental data on hadron–nucleus interactions in the energy range from AGS to SPS are reviewed. Emphasis is put on a comparison with both hadron–hadron and nucleus–nucleus collisions data. Arguments for an extension of hadron–nucleus collision programme into the RHIC domain are given.

abstract

New NA49 data on baryon and anti-baryon production in nucleon + proton interactions demonstrate the importance of isospin effects and asymmetric baryon pair production. Consequences for the interpretation of baryon number transfer and central net baryon density are discussed.

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New data on identified baryons in the projectile hemisphere of \(p+p\) and centrality-selected \(p+{\rm Pb}\) and \({\rm Pb}+{\rm Pb}\) collisions are shown. Information from pion-induced interactions is used to isolate the projectile role in the observed phenomena. A common picture emerges for \(p+p\), \(p+{\rm Pb}\) and \({\rm Pb}+{\rm Pb}\) reactions: with increasing centrality, the projectile baryon number is strongly “pushed” towards the backward hemisphere of the collision. In the magnitude of this common effect, most central \({\rm Pb}+{\rm Pb}\) interactions occupy a medium position between \(p+p\) and central \(p+{\rm Pb}\) reactions.

abstract

We discuss the physics underlying event-by-event fluctuations in relativistic heavy ion collisions. We will argue that the fluctuations of the ratio of positively over negatively charged particles may serve as a unique signature for the Quark Gluon Plasma.

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Comparing quantities to analyze charged fluctuations in heavy ion experiments, the dispersion of the charges in a central rapidity box was found to be best suited. Various energies and different nuclear sizes are considered in an explicit Dual-Parton-Model calculation using the DPMJET code and a randomized modification to simulated charge equilibrium. For large enough detection regions charged particle fluctuations can provide a signal of the basic dynamics of heavy ion processes.

abstract

The net-baryon density at midrapidity is proposed as an order parameter in the search for the QCD critical point in heavy ion collisions. As a function of the initial energy and the total number of participants, this quantity obeys a scaling law, dictated by the critical exponents of the appropriate universality class. The corresponding scaling variable specifies the proximity of a given experiment to the critical point. Within this framework, measurements at the SPS are discussed and predictions for RHIC and LHC are extracted.

abstract

Internal microscopic symmetry of a many body system leads to global constraints. We obtain explicit forms of the global macroscopic condition assuring that at the microscopic level the evolution respects the overall symmetry.

abstract

We present two things in this discussion. First, we develop and prove the theory of the extension of the YFS Monte Carlo approach to higher order SU\(_{\rm 2L}\times {\rm U}_1\) radiative corrections to the analogous higher order QCD radiative corrections. Contact is made with other pioneering soft gluon resummation theories in the literature. Second, semi-analytical results and preliminary explicit Monte Carlo data are presented for the specific example of the processes \(p\bar {p}\rightarrow t\bar {t}+n(G)+X\) at FNAL energies, where \(G\) is a soft gluon and the respective event generator, ttp1.0, features realistic, event-by-event simulation of multiple, soft, finite \(p_{\rm T}\) gluon effects in which the infrared singularities are canceled to all orders in \(\alpha _s\). We comment briefly on the implications of our results on the CDF/D0 observations and on their possible applications to RHIC physics and to LHC physics.

abstract

A saturation model for the total \(\gamma \gamma \) and \(\gamma ^{*} \gamma ^{*}\) cross-sections and for the real photon structure function \(F_2^{\gamma }(x,Q^2)\) is described. The model is based on a QCD dipole picture of high energy scattering. The two-dipole cross-section is assumed to satisfy the saturation property with the saturation radius taken from the GBW analysis of the \(\gamma ^*p\) interaction at HERA. The model is combined with the QPM and non-pomeron reggeon contributions and it gives a very good description of the data on the \(\gamma \gamma \) total cross-section, on the photon structure function \(F_2^{\gamma }(x,Q^2)\) at low \(x\) and on the \(\gamma ^* \gamma ^*\) cross-section. Production of heavy quarks in \(\gamma \gamma \) collisions is also studied.

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In this talk the results of the analytical and numerical analysis of the nonlinear Balitsky–Kovchegov equation are presented. The characteristic BFKL diffusion into infrared regime is suppressed by the generation of the saturation scale \(Q_s\). We identify the scaling and linear regimes for the solution. We also study the impact of subleading corrections onto the nonlinear evolution.

abstract

A model for \(J\)/\({\mit \Psi }\) suppression at a high energy heavy ion collision is presented. The main (and the only) reason for the suppression is \(J\)/\({\mit \Psi }\) inelastic scattering within hadron matter. The hadron matter is in the form of an evolving multi-component point-like non-interacting gas. The estimations of the sound velocity in the gas and the approximate pattern of cooling caused by the longitudinal expansion are also presented. It is shown that under such circumstances and with \(J\)/\({\mit \Psi }\) disintegration in nuclear matter added, \(J\)/\({\mit \Psi }\) suppression evaluated agrees well with NA38 and NA50 data. Additionally, some rough estimations of \(J\)/\({\mit \Psi }\) suppression in hadron matter described in the framework of the excluded volume gas model are given.

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We considered the phenomenon of the Andreev reflection of quarks at the interface between the cold quark–gluon plasma phase and 2SC color superconductor.

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The application of statistical model in heavy ion collisions is discussed in the energy range from SIS/GSI through AGS/BNL up to SPS/CERN and RHIC/BNL. It is shown that in this broad energy range hadronic yields and their ratios resemble a thermal equilibrium population along a unified freeze-out curve determined by the condition of fixed energy per particle \(\simeq 1\) GeV. The role of exact conservation of quantum numbers in the kinetic description of rarely produced particles is also analyzed.

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The \(p_\perp \)-spectra of hadrons measured at RHIC are very well described in a model which assumes that the chemical and thermal freeze-outs occur simultaneously. The model calculation includes all hadronic resonances and uses a simple parametrization of the freeze-out hypersurface.

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The hydrodynamical models used to describe the evolution of heavy-ion collisions are briefly reviewed and their results compared with recent RHIC data.

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An overview of the prevailing experimental conditions at the CERN–LHC for heavy-ion collisions is given. Observables, in particular those unique to the LHC energy regime, are discussed. The experimental challenges and physics potential of detector subsystems — TPC and TRD — are reviewed in some detail.

abstract

The \(\cal {P}\cal {P}\)2\(\cal {P}\cal {P}\) experiment is devoted to the proton–proton elastic scattering measurements at the Relativistic Heavy Ion Collider (RHIC) at the center-of-mass energies \(50 \leq \sqrt {s} \leq 500 \) GeV and the four-momentum transfer \(0.0004 \leq |t| \leq 1.3\) \({\rm GeV}^{2}\). The option of polarized proton beams offers a unique possibility to investigate the spin dependence of the proton elastic scattering in a systematic way. The energy dependence of the total and elastic cross section, the ratio of the real to imaginary part of the forward scattering amplitude, and the nuclear slope parameter will be studied. In the medium \(|t|\) region (\(|t| \leq 1.3\) \({\rm GeV}^{2}\)) the energy dependence of the dip structure in the elastic differential cross section will be measured. With polarized beams the measurement of spin dependent observables: the difference of the total cross sections as functions of the initial transverse spin states, the analyzing power and the double spin asymmetries will be used to map the \(s\) and \(t\) dependence of the proton helicity amplitudes.

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A (very personal) summary of the meeting is presented.