Table of contents

This conference opening talk presents a short review of recent progress in strangeness production systematics, notably the topic of energy dependence, up to RHIC. The data are confronted with the statistical hadronization model which helps to answer the question of their connection to the parton–hadron phase transformation occuring at upper SPS energies.

We calculate the ϕ meson collision rate and mean free path in a hot hadronic gas. The hidden local symmetry model is used to take into account interactions of ϕ mesons with pseudoscalar (π, K) and vector mesons (ρ, ω, K*, ϕ). In contrast to previous calculations we find a significantly small mean free path (around 1 fm at T = 200 MeV). This implies that ϕ mesons produced after hadronization in relativistic heavy-ion collisions will not leave the collision region without scattering. The consequences of these findings to the analysis of ϕ yields are discussed.

The STAR detector has made a variety of measurements of strange and other hadronic species in Au+Au collisions at √s_NN = 130 GeV. A comparison of kaon and pion production enables an examination of the systematics of strangeness production with energy by comparing them to lower energy collisions. Anti-baryon to baryon ratios indicate a much reduced net-baryon density and transverse momentum spectra show that a picture of transverse expansion seems appropriate.

Strangeness production in microscopic transport models for relativistic heavy-ion collisions from SIS to RHIC is reviewed: after a brief introduction into elementary strangeness production processes, the main emphasis is put on strangeness as an indicator of the nuclear equation of state, the excitation function of the K⁺/π⁺ ratio and strangeness as a deconfinement indicator.

An analysis of hadron abundances in heavy ion collisions from SPS to RHIC energy within the statistical–thermal model is presented. Pb–Pb collisions at 40 A GeV are analysed for the first time here. Unlike as stated in similar recent studies, the data analysis rules out a complete strange chemical equilibrium in full phase space. In fact, the use of multiplicities integrated in full phase space or in a limited rapidity window at SPS energy gives rise to different results for the extra-strangeness suppression parameter γ_S while the extracted values of temperature and baryon-chemical potential do not vary significantly. This behaviour raises the question of whether the observed hadronic strangeness phase space saturation at RHIC within a small mid-rapidity window would hold in a possible full phase space analysis.

We utilize the ALCOR model for mid-rapidity hadron number predictions at AGS, SPS and RHIC energies. We present simple fits for the energy dependence of stopping and quark production.

The E895 Collaboration has investigated a number of mixed-particle correlations involving neutral strange particles (K⁰_s and Λ) in 2, 4, 6 and 8 A GeV Au + Au collisions at the AGS. The first measurements for pΛ correlations indicate a correlation magnitude of about 50% with a 26 MeV width. Detailed comparisons between data and theory suggest an emitting source with an effective Gaussian radius close to 4.5 fm. This radius is much larger than the value of 2.8 fm predicted by the relativistic transport code ART. Pairs of pK⁰, π^−Λ and π⁻K⁰ are found to display essentially zero correlation at 6 A GeV. The latter observations are not unexpected considering that the proton–K⁰ interaction has a very small scattering length and there are no very well known interactions between pions and Λs or K⁰s.

Recent work on chemical equilibrium in heavy-ion collisions is reviewed. The energy dependence of thermal parameters is discussed. The centrality dependence of thermal parameters at SPS energies is presented.

ALICE (a large ion collider experiment) will be the only detector dedicated to the study of nucleus–nucleus collisions at the LHC. The capabilities of ALICE to measure hidden and open heavy flavours are reviewed.

Heavy ion collisions at SIS energies (1–2 A GeV) offer a unique tool to probe the properties of hot and dense nuclear matter. In particular, the partial restoration of chiral symmetry is predicted to lead in this energy range to in-medium modifications of hadron properties. Strange particle production below or close to the threshold energy is a useful probe to investigate these in-medium effects. The FOPI collaboration has recently measured the production and the propagation of charged and neutral strange particles. The K⁺ production probability is investigated as a function of the system size at a beam energy of 1.5 A GeV. Results on K⁰ production as well as K⁻/K⁺ ratio as a function of rapidity in Ru+Ru collisions at 1.69 A GeV are presented. In addition, the sideward flow of charged and neutral strange particles has been measured. Results are compared with predictions of transport calculations (BUU and IQMD).

Preliminary results on the K*(892)⁰ → πK production using the mixed-event technique are presented. The measurements are performed at mid-rapidity by the STAR detector in √s_NN = 130 GeV Au–Au collisions at RHIC. The K*⁰ to negative hadron, kaon and ψ ratios are obtained and compared to the measurements in e⁺e⁻, pp and p at various energies.

The NA57 experiment has been designed to study the onset of enhanced production of strange baryons and anti-baryons in Pb–Pb collisions with respect to p–Be collisions. Results from 40 and 160 A GeV/c Pb–Pb data will be shown. The main focus is on the checks of the NA57 analysis chain.

The dependence of K⁺ production on the nuclear equation of state is investigated in heavy ion collisions. An increase in the excitation function of K⁺ multiplicities obtained in heavy (Au+Au) over light (C+C) systems when going far below the threshold which has been observed by the KaoS Collaboration, strongly favours a soft equation of state. This observation holds despite the influence of an in-medium kaon potential predicted by effective chiral models which is necessary to reproduce the experimental K⁺ yields. Phase space effects are discussed with respect to the K⁺ excitation function.

Two signatures of the quark–gluon plasma—strangeness 'enhancement' and J/ψ 'suppression'—in nucleus–nucleus collisions are critically discussed. A recently developed statistical coalescence model for J/ψ production is presented. The measurements at the RHIC energies are crucial for disentangling the different scenarios of J/ψ formation.

This paper is devoted to a review of the field of strangeness production in (ultra-)relativistic heavy ion collisions within our present theoretical understanding. Historically, there have been (at least) three major ideas for the interest in the production of strange hadronic particles: (1) mass modification of the kaons in a (baryon-)dense environment; (2) (early) K⁺-production probes the nuclear equation of state; (3) enhanced strangeness production especially in the (multi-)strange (anti)baryon channels as a signal of quark gluon plasma formation. As a guideline for the discussion, I employ the extensive experience with microscopic hadronic transport models. In addition, I elaborate on the recent idea of antihyperon production solely by means of multi-mesonic fusion-type reactions.

We discuss the theoretical description of kaon production at energies around the thresholds. Uncertainties in the interpretation of experimental data on K⁺ are caused by the parametrization of cross sections not accessible by experimental mesurements. However, the ratio of kaon yields obtained in different systems seems to be robust against these uncertainties. The production of K⁻ is strongly linked to the Λ yield and therefore reflects the problems in the description of K⁺ production.

The production of black holes at Tevatron and LHC in spacetimes with compactified space-like large extra dimensions is studied. Either black holes can already be observed in p collisions at √s = 1.8 TeV or the fundamental gravity scale has to be above 1.4 TeV. At LHC the creation of a large number of quasi-stable black holes is predicted, with lifetimes beyond several hundred fm/c.

A cut-off in the high-P_T jet cross section is shown to be a unique signature of black hole production. This signal is compared to the jet plus missing energy signature due to graviton production in the final state as proposed by the ATLAS collaboration.

Dynamics of the baryon number transport determine the mid-rapidity characteristics in nucleus–nucleus collisions: considerable net baryon densities at the AGS and SPS, and small but finite at RHIC. Fragmentations of incident baryons are used to describe the baryon number transport in nuclear collisions. We report results of leading proton, neutron and Lambda measurement in p+A collisions from E941 at the AGS. We discuss the impact of fragmentation schemes on baryon number transport and hyperon production in nuclear collisions.

Recent NA49 results on Λ, , Ξ⁻ and ⁺ production in minimum-bias p+p and centrality-selected p+Pb collisions at 158 GeV/c, and the results on Λ, , 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 Λ and 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 Λ/π ratio. K⁺/π at mid-rapidity is affected in a similar way, due to the associated production of K⁺ together with Λ 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.

We introduce a microscopic and relativistic theory describing free scattering and finite nuclei for the octet baryons in a consistent quantum field theoretical framework based on Dirac–Brueckner theory and nuclear mean field. In a first quantitative approach, yet still heuristic for dealing with the Λ hyperon, the quality of the description of finite (hyper)nuclei based on free meson exchange potentials is competitive with those from purely phenomenological relativistic mean-field calculations. In contrast to the latter our approach has the advantage of having a microscopic link to free interactions and complete control of which classes of diagrams are included. As a complementary way for determining hyperon–hyperon and hyperon–nucleon interactions the use of Hanbury–Brown–Twiss interferometry is discussed.

Recent results from the NA49 experiment on the energy dependence of charged kaon production in central Pb+Pb collisions are presented. First results from the new data at 80 A GeV beam energy are compared with those from lower and higher energies. A difference in the energy dependence of the ⟨K⁺⟩/⟨π⁺⟩ and ⟨K⁻⟩/⟨π⁻⟩ ratios is observed. The ⟨K⁺⟩/⟨π⁺⟩ ratio shows a non-monotonic behaviour with a maximum near 40 A GeV.

The production of ϕ(1020), Λ*(1520) and *(892) resonances at the final stage of a heavy-ion collision is considered. It is shown that original momentum distributions and abundance of resonances formed during the process of heavy-ion collisions may differ significantly from their measured spectra and yields. The reconstruction probability of resonances decaying inside the fireball can be strongly suppressed because of interactions of their hadronic decay products in the fireball medium. We investigate the dependence of the degree of suppression on the fireball size, dynamics and the resonance decay width in the medium. Quantitative results are presented for lead–lead collisions at 158 GeV SPS beam energy.

A brief summary of the theoretical speculations concerning strangelets and metastable multi-hypernuclear objects (MEMOs) as well as a short survey of the experimental results obtained at AGS and SPS in this research field are given. Then we examine the possibility of producing and evidencing such an exotic strange matter, also including pure hyperonic bound states ((ΛΛ)_b, (ΞΛ)_b), at RHIC and LHC. Simulations are presented to estimate the sensitivity of the STAR and ALICE experiments to the detection of these objects, focusing mainly on the metastable short-lived (weak-decaying) strange dibaryons, with a particular emphasis on the H-dibaryon, a six-quark-bag bound state (uuddss).

The nonmesonic decay of Λ hyperons has been investigated by the observation of delayed fission of heavy hypernuclei produced in proton–U collisions at T_p = 1.9 GeV. The lifetime of heavy hypernuclei with masses A ≈ 220 of the present work, τ_Λ = (138 ± 6 (stat) ± 17 (syst)) ps, is the most accurate result obtained in proton and antiproton induced collisions on a U target so far. This result together with the values of the lifetime measured previously by the COSY-13 collaboration, for p+Bi (161 ± 7(stat) ± 14(syst)) ps and p+Au (130 ± 13(stat) ± 15(syst)) ps, gives an average value for the lifetime of heavy hypernuclei with masses A > 180: τ_Λ = (145 ± 11) ps. This value was obtained by averaging the above lifetimes with weights taken as reciprocals of the sum of squares of statistical and systematic errors. By comparing the lifetimes of light and heavy hypernuclei we found—on the confidence level of 0.98—a violation of the phenomenological ΔI = 1/2 rule known from the weak mesonic decays of strange particles.

We report preliminary results on the centrality dependence of both Λ and production as a function of centrality at mid-rapidity in Au+Au collisions at √s_NN = 130 GeV in the STAR detector. Data are measured in five different centrality classes which cover the most central 75% of the cross-section. In the case of Λ and , the transverse mass spectra are best described by a Boltzmann function with inverse slope parameters which vary from ∼320 MeV in the most central collisions to ∼260 MeV in the non-central collisions. The K⁰_s, however, are best described by a simple exponential fit though their inverse slopes show the same behaviour, decreasing from ∼290 MeV to ∼270 MeV. It is also found that the yields of the K⁰_s, Λ and increase linearly with increasing multiplicity in the collision, while the /Λ shows no significant centrality dependence.

In this paper we review recent progress on the systematic evaluation of the kaon and antikaon spectral functions in dense nuclear matter based on a chiral SU(3) description of the low-energy pion–, kaon– and antikaon–nucleon scattering data.

Strange quark matter in a colour–flavour locked state is significantly more bound than 'ordinary' strange quark matter. This increases the likelihood of strangelet metastability or even absolute stability. Properties of colour–flavour locked strangelets are discussed and compared to ordinary strangelets. Apart from differences in binding energy, the main difference is related to the charge. A statistical sample of strangelets may allow experimental distinction of the two. Preliminary estimates indicate that the flux of strangelets in galactic cosmic rays could be sufficient to allow for strangelet discovery and study in the upcoming alpha magnetic spectrometer AMS-02 cosmic ray experiment on the International Space Station.

This contribution focuses on the results of statistical model calculations at RHIC energies, including recently available experimental data. Previous calculations of particle yield ratios showed good agreement with measurements at SPS and lower energies, suggesting that the composite system possesses a high degree of chemical equilibrium at freeze-out. The effect of feed-down contamination on the model parameters is discussed, and the sensitivity of individual ratios to the model parameters (T, μ_B) is illustrated.

The recent preliminary results from central Au+Au collisions at √s_NN = 130 GeV from the STAR experiment at RHIC are presented and discussed along with the results on the Λ(1520) production in cental Pb+Pb and p+p collisions at √s = 17 GeV from the NA49 experiment at the SPS. The Λ(1520) is measured with the invariant mass reconstruction of the decay products in the hadronic channel (K⁻, p). The mean Λ(1520) multiplicity scaled by the number of participants decreases from p+p to Pb+Pb collisions at the same energy of √s = 17 GeV. An upper limit estimate of the multiplicity from the first measurement at √s_NN = 130 GeV shows the same trend. Comparisons with model predictions provide an indication of possible medium effects on the resonances and their decay daughters.

In this paper we present recent results from the NA49 experiment for Λ and hyperons produced in central Pb + Pb collisions at 40, 80 and 158 A GeV. Transverse mass spectra and rapidity distributions for Λ 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 Λ/π at mid-rapidity and in 4π has a maximum around 40 A GeV. In addition, rapidity distributions have been measured at 40 and 80 A GeV, which allows us to study the /Λ ratio.

Recent results concerning the production of strangeness obtained by the PHENIX experiment from the first year of Au + Au collisions at √s_NN = 130 GeV at the RHIC facility at Brookhaven National Laboratory are presented. Single-particle spectra and the ratios of single-particle yields for pions, kaons and protons are discussed. The characteristics of these spectra are examined as a function of the number of participating nucleons in the collision and as a function of transverse momentum. The prospects for a measurement of charm observables in the full-energy √s_NN = 200 GeV Au + Au run at RHIC are discussed.

The production of K⁺ and K⁻ mesons in elementary proton–proton collisions has been investigated at the Cooler synchrotron COSY in Jülich. A high quality proton beam with low emittance and small momentum spread permitted study of the creation of these mesons very close to the kinematical threshold.

The energy dependence of the total cross section is investigated using internal beam facilities providing a high accuracy particle momentum determination as well as an external non-magnetic detection setup with a large geometrical acceptance. The determination of the four-momentum vectors for all ejectiles of each registered event gives the complete kinematical information allowing study of the interaction of the outgoing particles. Results on the performed studies of the pp → ppK⁺K⁻, pp → pΛK⁺ and pp → pΣ⁰K⁺ reactions will be presented and their relevance to the interpretation of heavy ion collisions will be discussed.

A review of meson emission in heavy-ion collisions at incident energies from SIS up to collider energies is presented. A statistical model assuming chemical equilibrium and local strangeness conservation (i.e. strangeness conservation per collision) explains most of the observed features.

Emphasis is put on the study of K⁺ and K⁻ emission at low incident energies. In the framework of this statistical model it is shown that the experimentally observed equality of K⁺ and K⁻ rates at 'threshold-corrected' energies √s − √s_th is due to a crossing of two excitation functions. Furthermore, the independence of the K⁺/K⁻ ratio from the number of participating nucleons observed between SIS and RHIC is consistent with this model.

It is demonstrated that the K⁻ production at SIS energies occurs predominantly via strangeness exchange and that this channel approaches chemical equilibrium. The observed maximum in the K⁺/π⁺ excitation function is also seen in the ratio of strange to non-strange particle production. The appearance of this maximum around 30 A GeV is due to the energy dependence of the chemical freeze-out parameters T and μ_B.

An overview of results for interactions of Au+Au ions at centre-of-mass energies of √s_NN = 56, 130 and 200 GeV obtained by the PHOBOS collaboration at RHIC is given. Measurements of primary charged particle density near mid-rapidity indicate that particle production grows logarithmically with collision energy and faster than linearly with the number of interacting nucleons. Elliptic flow is found to be much stronger at RHIC than at SPS energy. The effect is strongest in peripheral events and decreases for more central collisions and emission angles |η| > 1. The measured anti-particle to particle ratios of production rates for pions, kaons and protons in central Au+Au interactions at √s_NN = 130 GeV are compatible with the statistical model of particle production, showing an increasingly baryon-free region in mid-rapidity with the increase of collision energy.

The experiment NA50 studies the strangeness production by means of the BR^ϕ_μμσ_ϕ/(BR^ρ_μμσ_ρ + BR^ω_μμσ_ω) cross-sections ratio in relativistic heavy ion collisions with respect to proton and light ion collisions. New results for Pb+Pb interactions at 158 A GeV/c are presented (1998 data) and analysed with a different method. The BR^ϕ_μμσ_ϕ/(BR^ρ_μμσ_ρ + BR^ω_μμσ_ω) ratio shows an increase with the number of participants, in agreement with previous results. The inverse slope parameter extracted from the M_T universal scaling is also studied.

We study the canonical flavour enhancement arising from exact conservation of strangeness and charm flavour. Both the theoretical motivation, and the practical consequences are explored. We argue using qualitative theoretical arguments and quantitative evaluation, that this proposal to re-evaluate strangeness signature of quark–gluon plasma is not able to explain the majority of available experimental results.

In these remarks I explain the motivation which leads us to consider chemical non-equilibrium processes in flavour equilibration and in statistical hadroniziation of quark–gluon plasma (QGP). Statistical hadronization allowing for chemical non-equilibrium is introduced. The results of fits to RHIC-130 results, including multistrange hadrons, are shown to agree only with the model of an exploding QGP fireball.

Results from the BRAHMS Collaboration for the inaugural physics run with the relativistic heavy ion collider (RHIC), Au + Au collisions at √s_NN = 130 GeV in the late summer of 2000, and some results of the very first data from the summer of 2001 at √s_NN = 200 GeV are presented. Here the main focus is on the determination of the pseudorapidity distribution of charged particles as a function of collision centrality and on the measurement of the antiproton to proton and the K⁻ to K⁺ ratios as a function of rapidity. The pseudorapidity density at midrapidity reaches dN(ch)/dη = 553 ± 36 for the most central collisions (0–5%) at √s_NN = 130 GeV; the corresponding number for a higher energy is dN(ch)/dη = 632 ± 36, demonstrating an increase in multiplicity of about 14%. The measured antiproton/proton ratios peak at midrapidity around N()/N(p) = 0.64 ± 0.06 and drop to 0.41 ± 0.04 at y ≈ 2 for √s_NN = 130 GeV reactions; the K⁻ to K⁺ ratios are 0.90 ± 0.06 (y ≈ 0) and 0.83 ± 0.1 (y ≈ 2.5).

The equation of state for compact stars is reviewed with special emphasis on the role of strange hadrons, strange dibaryons and strange quark matter. The implications for the properties of compact stars are presented. The importance of neutron star data to constrain the properties of hypothetical particles and the possible existence of exotic phases in dense matter are outlined. We also discuss the growing interplay between astrophysics and heavy-ion physics.

During the 1999 lead run, CERES has measured hadron and electron-pair production at 40 A GeV/c beam momentum with the spectrometer upgraded by the addition of a radial TPC. Here the analysis of Λ and will be presented.

A major field of research at the future accelerator facility at GSI will be the exploration of the QCD phase diagram in the region of high baryon densities. This approach is complementary to the studies of matter at high temperatures performed at the CERN-SPS, RHIC and the future LHC. Experimental observables and the proposed detector system will be discussed.

The properties of plasmons, Nambu–Goldstone bosons and gapless Carlson–Goldman collective modes in colour–flavour locked phase of colour superconducting dense quark matter at finite temperature are reviewed. A possibility of a kaon condensation with an abnormal number of NG bosons is also discussed.

We make predictions for the kaon interferometry measurements in Au+Au collisions at the relativistic heavy ion collider (RHIC). A first-order phase transition from a thermalized quark–gluon plasma (QGP) to a gas of hadrons is assumed for the transport calculations. The fraction of kaons that are directly emitted from the phase boundary is considerably enhanced at large transverse momenta K_T ∼ 1 GeV/c. In this kinematic region, the sensitivity of the R_out/R_side ratio to the QGP properties is enlarged. The results of the one-dimensional correlation analysis are presented. The extracted interferometry radii, depending on K_T, are not unusually large and are strongly affected by finite momentum resolution effects.

The production and propagation of kaons and antikaons in relativistic heavy-ion collisions have been systematically investigated with the Kaon spectrometer at SIS/GSI. Experimental results on the K⁺ and K⁻ yield and on the azimuthal emission pattern of K⁺ mesons are presented. Within the framework of transport models the data can be explained assuming in-medium kaon–nucleon potentials. The comparison of K⁺ production excitation functions obtained for Au+Au and C+C collisions with results of transport model calculations favours a soft nuclear equation-of-state.

The heavy quark system is an excellent probe for learning QCD dynamics at finite density. First, we discuss the properties of the J/ψ and D mesons at finite nucleon density. We discuss why their properties should change at finite density and then introduce an exact QCD relation among these hadron properties and the energy momentum tensor of the medium. Secondly, we discuss attempts to calculate the Charmonium–hadron total cross section using effective hadronic models and perturbative QCD. We emphasize a recent calculation, where the cross section is derived using the QCD factorization theorem. We conclude by discussing some challenges for SIS 200.

We describe how the abundance and distribution of hyperon resonances can be used to probe freeze-out conditions. We demonstrate that resonance yields allow us to measure the time scales of chemical and thermal freeze-outs. This should permit a direct differentiation between the explosive, sudden and staged adiabatic freeze-out scenarios. We then discuss the meaning of recent experimental results and suggest further measurements.

The NA52 experiment searched for long-lived charged strangelets in 158 A GeV/c Pb+Pb collisions at CERN SPS. We collected 10¹³ Pb+Pb interactions looking for negatively charged strangelets and 3 × 10¹¹ Pb+Pb interactions for positively charged ones. No evidence for the production of strangelets has been observed. The upper strangelet production limits are discussed. Besides the strangelet searches NA52 was able to identify particles and anti-particles over a wide range in rapidity. Results of the invariant differential particle production cross sections including fragments up to carbon and 5 are presented.

No conventional picture of nucleus–nucleus collisions has yet been able to explain the abundance of Ω and hadrons in central collisions between Pb nuclei at 158 A GeV at the CERN SPS. We argue that this is evidence that they are produced from topological defects in the form of skyrmions arising from the formation of disoriented chiral condensates. It is shown that the excess Ω or produced could not be easily washed out in the hadronic medium and therefore would survive in the final state.

We present a phenomenological model describing the formation of a quark–gluon plasma (QGP) fireball in the very forward, baryon-rich rapidity region in nucleus–nucleus interactions, and its subsequent decay into baryons and possibly strangelets. The model explains the centauro events observed in cosmic rays and the long-penetrating component frequently accompanying them, and makes predictions for the LHC. We describe the CASTOR calorimeter, a subdetector to probe the very forward, baryon-rich rapidity region in Pb + Pb collisions at the LHC. The simulated response of the calorimeter to new effects is presented and its sensitivity is derived using a neural network technique.

We discuss the leading twist QCD prediction of the heavy-quarkonium hadron cross section. The energy dependence of the J/ψ–proton cross section is computed. It turns out to be small in the vicinity of the threshold and smoothly increases at high energy.

We investigate antikaon condensation in compact star matter using a relativistic mean field model. Antikaon condensates make the equation of state softer resulting in a smaller maximum mass star compared to the case without condensate. It is found that the equation of state including antikaon condensates gives rise to a stable sequence of compact stars called the third family beyond the neutron star branch.

Interactions of charmed and strange mesons with baryonic matter can be calculated in the nonrelativistic quark potential model. For KN scattering data exist, and the theoretical results for S-waves are in approximate agreement with experiment. Here we apply the same model to the scattering of open-charm (D) mesons by nucleons, and give quark model predictions for DN scattering amplitudes. Spin–orbit forces in KN and DN will also be discussed.

We investigate the in-medium modification of the charmonium breakup processes due to the Mott effect for light (pi, rho) and open-charm (D, D*) quark–antiquark bound states at the chiral/deconfinement phase transition. The Mott effect for the D-mesons effectively reduces the threshold for charmonium breakup cross sections, which is suggested as an explanation of the anomalous J/ψ suppression phenomenon in the NA50 experiment. Further implications of finite-temperature mesonic correlations for the hadronization of heavy flavours in heavy-ion collisions are discussed.

The Ω⁺/Ω⁻ ratio originating from string decays is predicted to be > 1 in pp interaction at SPS energies. The anti-Ω dominance increases with decreasing beam energy. This surprising behaviour is caused by the combinatorics of quark–antiquark production in small, finite strings. Since this behaviour is not found in a statistical description of hadron production in pp collisions, it may serve as a potent observable to probe the hadronization mechanism in such collisions.

We discuss the status of thermal model descriptions of particle ratios in central nucleus–nucleus collisions at ultra-relativistic energy. An alternative to the 'Cleymans–Redlich' interpretation of the freeze-out trajectory is given in terms of the total baryon density. Emphasis is placed on the relation between the chemical equilibration parameters and the QCD phase boundary. Furthermore, we trace the essential difference between thermal model analyses of data from collisions between elementary particles and from heavy ion collisions due to a transition from local strangeness conservation to percolation of strangeness over large volumes, as occurs naturally in a deconfined medium. We also discuss predictions of the thermal model for composite particle production.

Anisotropic flow of Ks, s and Λs is studied in heavy-ion collisions at SPS and RHIC energies within the microscopic quark–gluon string model. At SPS energy the directed flow of kaons differs considerably at midrapidity from that of antikaons, while at RHIC energy kaon and antikaon flows coincide. The change is attributed to the formation of dense meson-dominated matter at RHIC, where the differences in interaction cross-sections of hadrons become unimportant. The directed flows of strange particles, v₁^K,,Λ (y), have universal negative slope at |y| ⩽ 2 at RHIC. The elliptic flow of strange hadrons is developed at midrapidity at times 3 ⩽ t ⩽ 10 fm/c. It increases almost linearly with rising p_t and stops rising at p_t ⩾ 1.5 GeV/c reaching the same saturation value v₂^K,Λ(p_t) ≈ 10% in accord with experimental results.

A popular derivation of the apparent temperature of the particle transverse momentum spectra and its inconsistency are considered. An improved formula for the apparent temperature is discussed. It is shown that recent results on transverse mass spectra of J/ψ and ψ' mesons support a hypothesis of statistical production of charmonia at hadronization and suggest the early thermal freeze-out of these mesons. Using the apparent temperature formula the collective transverse velocity of the hadronizing quark gluon plasma is extracted to be ⟨v_T⟩ ≈ 0.2. Predictions for transverse mass spectra of hidden and open charm mesons along with bottomonium at SPS and RHIC energies are discussed.

We report preliminary results on production of multi-strange Ξ⁻ and their anti-particles, ⁺, at mid-rapidity in √s_NN = 130 GeV Au + Au collisions from the STAR experiment. An exponential fit to the Ξ⁻ transverse mass spectrum for the 14% most central collisions results in an inverse slope parameter T = 346 ± 7 MeV, an invariant yield dN/dy = 3.07 ± 0.13 (stat) and a non-identical particle ratio Ξ⁻/Λ = 0.244 ± 0.011. The multi-strange baryon production with respect to negative hadrons is found to be Ξ⁻/h⁻ = 0.0122 ± 0.0006.

Abundances of hadrons created in heavy ion collisions are surprisingly well described both by thermal and coalescence models. Instead of siding with any of the approaches, the causes of the good performance are studied, and possibilities of working out more basic hadronization models are discussed.

Final state interactions on the hadron spectra obtained from the MIcroscopic COalescence Rehadronization (MICOR) model are investigated. MICOR generates baryon and meson resonances in out-of-equilibrium distribution, directly from quark matter. At the next step, resonances are decayed into stable hadrons by the JETSET event generator. Then final state interactions are simulated using a hadronic cascade, with initial momentum distributions given by MICOR. For the initial space distributions, two simple models are applied and compared.

We discuss the production mechanism of partons via vacuum polarization during the very early, gluon-dominated phase of an ultrarelativistic heavy-ion collision in the framework of the background field method of quantum chromodynamics.

We investigate the production of heavy vector mesons with s, c and b contents. Starting from a factorization of the full transition amplitude into a hard production amplitude and soft initial and final state interactions, we employ the exchange of three gluons or an instanton 4q q interaction for the production mechanism. The structure of the mesons produced and the interacting protons are formulated as constituent q or quark–scalar diquark systems in a covariant relativistic quark model. As an upper limit, we find a typical suppression of the total threshold charm and bottom cross section relative to ϕ(1020) production by typically two and five orders of magnitude, respectively; the proper inclusion of effects from Lorentz contraction and the deformation of the interacting proton turns out to be of significant importance.

At the Kaon spectrometer KaoS at SIS/GSI, the production of kaons and antikaons in heavy-ion reactions at a beam energy of 1.5 A GeV has been measured for the collision systems Ni + Ni and Au + Au. The K⁻/K⁺ ratio is found to be constant for both systems and as a function of impact parameter but the slopes of K⁺ and K⁻ spectra differ for all impact parameters. Furthermore, the respective polar angle distributions will be presented as a function of centrality.

Using an extended version of the Nambu–Jona–Lasinio model we build a simple description of the baryons as diquark–quark bound states. First, a description of the diquarks in a dense and hot medium is presented. Then, we introduce the formalism for the baryons based on the Faddeev equation associated with the so-called 'static approximation' which finally gives a Bethe–Salpeter equation in the diquark–quark channel. By identifying the baryons with the bound states, we can obtain a description of their properties. In particular, we obtain the right mass spectrum for the proton, Λ, Ξ and Σ at T = 0 and μ = 0. We extend the formalism to finite temperature and density to obtain a description of the mass change of these baryons in the medium.

Phase transitions can be triggered by a change of density profile in neutron stars as a result of spin-up caused by mass accretion from a companion star. Such a spin evolution is the pathway from old canonical pulsars to millisecond pulsars. A number of x-ray neutron stars have been recently observed by the Rossi x-ray timing explorer (RXTE). Most of their frequencies are clustered in a narrow band with a few at higher frequency. This is the expected signature of a phase transition in the stellar core.

We show how to incorporate separate chemical and thermal freeze-outs consistently in a hydrodynamical code via a modified equation of state (general case) or via a modified Cooper–Frye formula (particular case of T_ch.f. close to T_th.f. or few particle species undergoing early chemical freeze-out). We find that separate freeze-outs may cause faster cooling of the fluid and affect predicted values of observables such as abundances.

The preliminary experimental data on ϕ production in the reaction Ni(1.93 A GeV) + Ni point to a puzzling high ϕ yield, which cannot be reproduced with present transport codes. We survey the experimental situation and present prospects for dedicated measurements of the ϕ multiplicities with the K⁺K⁻ and e⁺e⁻ channels at HADES and FOPI.

Enforcing exact conservation laws instead of average laws in statistical thermal models for relativistic heavy ion reactions gives rise to the so-called canonical effect, which can be used to explain some enhancement effects when going from elementary (e.g. pp) or small (pA) systems towards large AA systems. We review the recently developed method for the computation of canonical statistical thermodynamics, and give an insight into when this is needed in the analysis of experimental data.

Production of open and hidden charm hadrons in heavy-ion collisions is considered within the statistical coalescence model. Charmed quarks and antiquarks are assumed to be created at the initial stage of the reaction and their number is conserved during the evolution of the system. They are distributed among open and hidden charm hadrons at the hadronization stage in accordance with laws of statistical mechanics. The model is in excellent agreement with the experimental data on J/ψ production in lead–lead collisions at CERN SPS and predicts strong enhancement of the open charm multiplicity over the standard extrapolation from nucleon–nucleon to nucleus–nucleus collisions. A possible mechanism of the charm enhancement is proposed.

We present the first measurement of the ϕ vector meson production in Au + Au collisions at √s_NN = 130 GeV. For the top 11% multiplicity events, fitting an exponential to the transverse mass distribution, we obtain an inverse slope parameter of T = 379 ± 50 (stat) ± 45 (syst) MeV, a yield of dN/dy = 5.73 ± 0.37 (stat) ± 0.69 (syst) per event and a N_ϕ/N_h⁻ ratio of (2.1 ± 0.1 (stat) ± 0.4 (syst))%. Within the statistical error we find no dependence of the inverse slope parameter, T, or the N_ϕ/N_h⁻ ratio on multiplicity.

Non-Abelian energy loss in quark–gluon plasma is shown to lead to novel hadron ratio suppression patterns in ultrarelativistic nuclear collisions. We apply recent (GLV) estimates for the gluon radiative energy loss, which increases linearly with the jet energy up to E < 20 GeV and depends quadratically on the nuclear radius, R. The K⁺/π⁺ ratio is found to be most sensitive to the initial density of the plasma.

The structure of a spherically symmetric stable dark 'star' is discussed, at zero temperature, containing (1) a core of quarks in the deconfined phase and antileptons, (2) a shell of hadrons in particular n, p, Λ and Σ⁻ and leptons or antileptons and (3) a shell of hydrogen in the superfluid phase. If the superfluid hydrogen phase goes over into the electromagnetic plasma phase at densities well below one atom/(10 fm)³, as is usually assumed, the hydrogen shell is insignificant for the mass and the radius of the 'star'. These quantities are then determined approximately: mass = 1.8 solar masses and radius = 9.2 km. In contrast, if densities of the order of one atom/(10 fm)³ do form a stable hydrogen superfluid phase, we find a large range of possible masses from 1.8 to 375 solar masses. The radii vary accordingly from 9 to 1200 km.

The first measurements of kaon phase space densities are presented as a function of m_T, √s_nn and the number of participants. The kaon phase space density increases with the number of participants from e⁺e⁻ to Pb + Pb collisions. However, the ratio of the kaon and pion phase space densities at low p_T is independent of the number of participants for √s_nn = 17 GeV.

We study a neutron star model based on phenomenological equations of state including a phase transition between the hadronic phase and the quark–gluon plasma with two and three flavours. The results indicate the possibility of a 'cascade' type of transformation of neutron stars to hybrid stars with ud- and uds-quark matter cores.

On the basis of lattice calculations, we require the existence of a deconfined quark matter region (0 < a_s < 1) beyond the hadron gas phase, which goes asymptotically into the ideal quark–gluon plasma domain, in the phase diagram of nuclear matter. We consider empirically the dynamics of this region in terms of the order parameters and mass-scaled partition functions and derive an EoS. Then, the strange-quark chemical potential is expressed in a functional form of the temperature and light-quark chemical potential and its variation throughout the 3-region phase diagram is studied. We propose the change of the sign of the strange-quark chemical potential, from positive in the hadronic region to negative beyond, to be a unique, concise and well-defined indication of the quark-deconfinement phase transition in nuclear matter. Analysis of the nucleus–nucleus collision data from AGS and SPS is presented giving strong support to our proposal.

We present preliminary results of the charged kaon correlation analysis of Au + Au collisions at √S_NN = 130 GeV performed by the STAR Collaboration at RHIC. RHIC data are compared with SPS results as well as theoretical predictions.

We report STAR results on the azimuthal anisotropy parameter v₂ for strange particles K_S⁰ and Λ at mid-rapidity in Au + Au collisions at √s_NN = 130 GeV at RHIC. The value of v₂ as a function of transverse momentum p_t and collision centrality is presented for both particles and compared with model calculations. A strong p_t dependence in v₂ is observed up to p_t ∼ 2.0 GeV/c where v₂ begins to saturate.

We discuss the statistical model description of particle production in heavy-ion collisions. We put particular emphasis on the interpretation of the enhancement of particles that carry a non-vanishing quantum number related to U(1) internal symmetry. We argue that the basic features of experimental data showing enhancement of strange mesons and baryons are well described by the model.

The STAR experiment at RHIC is capable of a wide variety of measurements of the production of strange hadrons in nuclear collisions. Measurements of the relative production of strange baryons, antibaryons and kaons can shed light on the baryon densities achieved in these collisions and on the validity of models for production yields. We will present here preliminary results on these measurements at RHIC energies of √s_NN = 130 GeV and 200 GeV and discuss comparisons to models.

It is observed that K⁻/π in A + A and possibly p + p and + p collisions follows interesting systematics in ω, the pion transverse energy per unit of rapidity and transverse overlap area. The systematics show a linear increase of K⁻/π with ω in the AGS and SPS energy regime and a saturation at RHIC energy. The systematics indicate that ω might be the relevant variable underlying K⁻/π. At high energy, the ω variable is related to the gluon saturation scale in high density QCD, and perhaps to the initial energy density in the Bjorken picture.

We derive the kinetic equation for pure gluon QCD plasma, applying the background field method. The derivation is quite general and is not limited to the vicinity of equilibrium as it was assumed in earlier work. We show that the quantum kinetic equation contains a term, as in the classical case, that describes a colour charge precession of partons moving in the gauge field. We emphasize that this new term is necessary for the gauge covariance of the resulting equation.

We discuss the dynamical effects of strangeness and charm production in high-energy nuclear collisions. In order to understand the early stage dynamical evolution, it is necessary to study the transverse momentum distributions of multi-strange hadrons such as Ξ and Ω and charm mesons such as J/Ψ as a function of collision centrality.

The experimental data on hadron yields and ratios in central Pb + Pb and Au + Au collisions at SPS and RHIC energies, respectively, are analysed within a two-source statistical model of an ideal hadron gas. These two sources represent the expanding system of colliding heavy ions, where the hot central fireball is embedded in a larger but cooler fireball. The volume of the central source increases with rising bombarding energy. Results of the two-source model fit to RHIC experimental data at midrapidity coincide with the results of the one-source thermal model fit, indicating the formation of an extended fireball, which is three times larger than the corresponding core at SPS.

Within a BUU type transport model we study ϕ meson production in subthreshold Ni + Ni and Ru + Ru reactions. For the first time we included in our model the elementary reaction channels ρ + N, Δ → ϕ + N, π + N(1520) → ϕ + N and πρ → ϕ. In spite of a substantial increase of the ϕ multiplicities by these channels, our results stay significantly below the preliminary experimental data.

International Advisory Committee

Aichelin Nantes F Antinori CERN J Cleymans Cape Town J-P Coffin IRES Strasbourg L P Csernai Bergen C Greiner Giessen H Gutbrod Nantes T Hallman Brookhaven J Harris Yale U Heinz Columbus, Ohio W Henning GSI P Jacobs LBL Berkeley S Kabana Bern B Kinson Birmingham V Koch LBL Berkeley R Lacey Stony Brook J Madsen Aarhus M Morando Padova B Müller Duke J Nagle Columbia G Odyniec Berkeley H Oeschler Darmstadt A Panagiotou Athens J Pochodzalla Mainz K Pretzl Bern E Quercigh CERN J Rafelski Arizona D Rischke Frankfurt G Roland MIT J Sandweiss Yale J Schaffner-Bielich Brookhaven S Schramm Frankfurt P Seyboth MPI Munich P Sonderegger CERN G Stephans MIT H Stöcker Frankfurt H Ströbele Frankfurt E Suhonen Oulu W Zajc Columbia J Zimanyi Budapest

Organizing Committee

P Braun-Munzinger GSI M Frey Frankfurt B Friman GSI M Gazdzicki Frankfurt W Greiner (Honorary Chair) Frankfurt S Hofmann Frankfurt S Hossenfelder Frankfurt G Münzenberg GSI K Paech Frankfurt J Reinhardt Frankfurt D Rischke Frankfurt P Senger GSI R Stock (Honorary Chair) Frankfurt H Stöcker (Chair) Frankfurt H Ströbele Frankfurt J Wambach Darmstadt