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FAIRNESS 2019, Genova, Italy, 20 May 2019 - 25 May 2019; Journal of physics / Conference series 1667, 012041 (2020). doi:10.1088/1742-6596/1667/1/012041, Published by IOP Publ.39969, Bristol

ALICE has observed that the relative fraction of strange hadrons grows strongly with multiplicity in small collision systems (proton-proton and proton-lead collisions) at LHC energies, in particular for multi-strange baryons. This implies that a proton-proton collision cannot be described as an incoherent sum of parton-parton collisions, an idea that has been central in most proton-proton generators, for example PYTHIA. To accommodate the new ALICE results, models have to introduce significant final-state interactions. These final-state effects can have very different phenomenological origin. To be able to eventually discriminate experimentally between different final-state models, new experimental tools are required and in this paper different multi-differential observables will be tested with this goal in mind. Transverse Spherocity (SO ) is an observable that allows a topological selection of events that are “isotropic” (dominated by multiple soft processes) and “jetty” (where a single hard process is responsible for a significant part of the multiplicity). The underlying event activity is another observable that can be used to vary the amount of soft processes. It can be estimated by measuring the charged-particle multiplicity in the Transverse region (RT ). Using these new observables, ALICE has obtained results for π, K, φ, p, and Ξ production at mid-rapidity ( | η | < 0.8 ) as a function of event shape and underlying event activity in proton-proton collisions at ( S N N ) = 13 TeV . Finally, this contribution will report on how these new multi-differential measurements compare to predictions from PYTHIA and EPOS-LHC.

Measurements of short-lived hadronic resonances are used to probe the properties of the hadronic phase in ultra-relativistic heavy-ion collisions. Since these resonances have lifetimes comparable to that of the produced fireball, they are sensitive to the competitive rescattering and regeneration effects in the hadronic gas, which modify the observed particle momentum distributions and yields after hadronization. Having different masses, quantum numbers, and quark content, hadronic resonances can provide insight into processes that determine the shapes of particle momentum spectra, strangeness production, and the possible onset of collective effects in small systems. We here present the latest results on ρ(770)0, K*(892), φ(1020), Σ(1385)±, Λ(1520), Ξ(1530)0 and Ξ(1820) production in pp, p–Pb, Pb–Pb and Xe–Xe collisions at different LHC energies. Results include system-size and collision-energy evolution of transverse momentum spectra, integrated yields, mean transverse momenta, particle ratios, and nuclear modification factors.

The study of the formation of a dense and hot baryonic matter is the main goal of exploration for the NICA/MPD project. Strangeness production in nuclear collisions is a key part of the MPD project physics program and is an important tool for studying the QCD phase diagram. An overview of the relevant characteristics for hypernuclei reconstruction in the NICA energy range with the simulated MPD detector are presented. Focus is put on invariant mass distributions, reconstruction efficiency and expected yields.

The PANDA experiment will be one of the pillars of the new Facility for Antiproton and Ion Research (FAIR), which is currently under construction in Darmstadt, Germany. PANDA will be a fixed-target experiment which will allow the study of non-perturbative phenomena of the strong interaction. These will be probed in antiproton-proton collisions in the momentum range of 1.5 - 15 GeV/c. Within the PANDA physics program, strangeness production will be addressed through p ¯ p → Y ¯ Y processes. Measurements of the p ¯ p → ∑ ¯ 0 Λ channel for its comparison with the existing data of the Λ ¯ Λ channel are highly encouraged to study the role of isospin symmetry in hadron production dynamics. This work consists on a simulation study focusing on the feasibility of measuring the p ¯ p → ∑ ¯ 0 Λ channel at PANDA.

We explore production mechanism and final state interaction in the $pp \to nK^ + \Sigma ^ +$ channel based on the inconsistent experimental data published respectively by COSY-11 and COSY-ANKE. The scattering parameter $a> 0$ for $n\Sigma ^ +$ interaction is favored by large near-threshold cross section within a nonrelativistic parametrization investigation, and a strong $n\Sigma ^ +$ interaction comparable to $pp$ interaction is also indicated. Based on this analysis we calculate the contribution from resonance $\Delta ^* (1920)$ through $\pi ^ +$ exchange within resonance model, and the numerical result suggests a rather small near-threshold total cross section, which is consistent with the COSY-ANKE data. With an additional sub-threshold resonance $\Delta ^*(1620)$, the model gives a much better description to the rather large near-threshold total cross section published by COSY-11.

The reaction pp->p K0 pi+ Lambda has been studied with the ANKE spectrometer at COSY-Juelich at a beam momentum of 3.65 GeV/c in order to search for a possible signal of the pentaquark Theta+(1540), decaying into the p K0 system. By detecting four charged particles in the final state, the K0 and the Lambda have been reconstructed to tag strangeness production. It has been found that the pi+ Lambda missing-mass spectrum displays no significant signal expected from the Theta+(1540) excitation. The total cross section for the reaction pp->p K0 pi+ Lambda has been deduced, as well as an upper limit for the Theta+ production cross section. The intermediate Delta++ K0 Lambda state is found to provide a significant contribution to the reaction., Comment: 10 pages, 7 figures; text changed, references added, style file changed

The BRAHMS experiment at RHIC has measured the rapidity distribution of charged pions, kaons and (anti-)protons in d+Au and p+p collisions at . The transverse momentum spectra of K±, π± and p at different rapidities will be presented. The rapidity dependence of particle ratios, such as like-particle ratios, K/π ratios and p/π ratios, in p+p collisions at is studied. The measured net-proton yields (stopping) are compared to models.

Quarks of other flavours than up and down, i.e. s, c and b quarks, have been long recognized as effective probes of the structure of hot QCD matter. In this paper, I review some of the motivations for their investigation and discuss the salient results obtained so far, with a focus on the results from the Relativistic Heavy-Ion Collider (RHIC). Some ideas for future studies are also mentioned.

We present a summary of measurements of strange particles performed by the experiment NA49 in central and minimum bias Pb+Pb collisions in the beam energy range 20A - 158A GeV. New results on Xi production in central Pb+Pb collisions and on Lambda, Xi production in minimum bias collisions are shown. Transverse mass spectra and rapidity distributions of strange particles at different energies are compared. The energy dependence of the particle yields and ratios is discussed. NA49 measurements of the Lambda and Xi enhancement factors are shown for the first time.

A short review of main results from the strangeness production study in heavy-ion collisions at the CERN SPS is presented.

The advent of RHIC has opened up the possibilities for a greater understanding of the hadronization process in relativistic heavy ion collisions. The large volume of data collected, together with high collisions energies, allows us to address both strangeness and charm production in great detail. This paper will present results on bulk strangeness production in Au+Au collisions at √ sNN = 200 GeV, in particular on strangeness enhancement and strange quark scaling. Also presented are results on strange particle ratios and elliptic flow measurements in the intermediate pT region, together with comparisons with theoretical models. An excitation function of strangeness yields and ratios are also presented with reference to the newly acquired Au+Au data at √ sNN =6 2.4 GeV. Also presented in this paper are the first results on charm production measured in STAR. Utilising the methods of reconstructing D mesons through their leptonic channels, the crosssection for charm production in d+Au collisions at √ sNN = 200 GeV is presented. Also shown is a first measurement of the elliptic flow of charmed mesons.

The reaction of pp -> pK(+)Lambda is a very good channel to study N-* resonances through their K Lambda decay mode, because there is no mixing of isospin I = 1/2 and I = 3/2 due to isospin conservation. In this work, we extend a resonance model, which can reproduce the total cross section very well, to offer differential cross section information about this reaction. It can serve as a reference to build the scheduled hadron detector at Lanzhou Cooler Storage Ring (CSR). Experiment measurement of these differential cross sections in the future will, supply us more constraints on the model and help us understanding the strangeness production dynamics better.

The pp→nK+Σ+ reaction is a very good isospin 3/2 filter for studying Δ++* decaying to K+Σ+. The proton beam experiment with a scheduled 4π hadron detector at Lanzhou Cooler Storage Ring (CSR) will make the study of this reaction possible. Here, based on very limited available knowledge on the relevant ingredients for this reaction, we give theoretical prediction with Monte Carlo simulation for various observables for this reaction. This could serve as a reference for building the scheduled hadron detector and for identifying new physics in the following-on experiments at CSR.

I discuss strangeness as a tool for studying the reaction and hadronization dynamics of relativistic heavy-ion collisions at RHIC. In particular, I focus on quark-number scaling of elliptic flow as a tool to determine the nature of hadronization as well as to quantify the amount of collective flow the strange quarks carry and discuss the use of (multi-)strange hadron radial flow and interferometry for characterizing the collective expansion and emitting source dimensions of a hadronizing quark-gluon-plasma.

In this survey, the topics which can be addressed through a study of strange particle production in ALICE are reviewed. The current status of the experiment as regards selection methods for hyperons and resonances are described.

The production yields and the directed flow of the neutral strange particles K0S and Λ(Λ0 + Σ0) have been measured with the FOPI detector at SIS/GSI in Ni+Ni collisions of 1.93 A GeV energy. For the K0, the distributions of the inverse slope parameter and the particle yield show good agreement with the results of previous K+ measurements. Furthermore, the directed flow patterns of K0 and K+ are found to be compatible. The comparison of Λ and proton exhibits a significant difference in the yield distribution whereas both particle species show the same flow behaviour.

Strange quark production in Au–Au collisions at RHIC is studied in the framework of the parton cascade model (PCM). The yields of (anti-) strange quarks for three production scenarios—primary–primary scattering full scattering and full production—are compared to a proton–proton baseline. Enhancement of strange quark yields in central Au–Au collisions compared to scaled p–p collisions increases with the number of secondary interactions. The centrality dependence of strangeness production for the three production scenarios is studied as well. For all production mechanisms, the strangeness yield increases with (Npart)4/3. The perturbative QCD regime described by the PCM is able to account for up to 50% of the observed strangeness at RHIC.

We have measured the rapidity distributions dN/dy of charged hadrons, in particular kaons, in central Au+Au collisions at s NN = 200 GeV. Preliminary transverse momentum spectra at √s NN = 62.4 GeV are also presented. This new measurement is used to complete and further discuss the energy and rapidity systematics of strangeness production and its dependence on the variations of the baryo-chemical potential.

A review of recent NA57 results on K 0 S and hyperon production from Pb-Pb collisions at 40 and 158 A GeV/c is presented. An energy and centrality dependence of particle yields, strangeness enhancements as well as transverse mass spectra at mid-rapidity are discussed.

The BRAHMS experiment at RHIC has measured pions, kaons and protons and their antiparticles over a wide range of rapidity and transverse momenta. Au+Au collisions, d+Au and p+p interactions have been studied. From the netproton rapidity distribution, a stopping power of 73% can be deduced for central Au+Au collisions. The rapidity distributions of produced particles exhibit Gaussian shapes. The full phase-space K + /π + ratio is 0.173 ± 0.003 ± 0.014 and the value for K - /π - is 0.143 ± 0.003 ± 0.011. At forward rapidities, the ratios for the positively and negatively charged mesons diverge and approach values similar to the ones measured at the SPS. New data at 62.4 GeV promise to shed light on the nature of the sharp maximum of the K + /π + ratio observed at low SPS energies. At midrapidity, the nuclear modification factor for central Au+Au collisions shows a strong pion suppression at intermediate transverse momenta; a suppression which is even stronger at forward rapidities. The nuclear modification factor for d+Au changes from a Cronin-like enhancement of charged hadrons at midrapidity to a suppression at forward rapidities.

We report on the transverse momentum dependence of strangeness production measured with the STAR detector. Identified particle spectra are used to provide a test of models of hadron production in the intermediate transverse momentum region, 2 < pT < 6 GeV/c. Further insight into hadron production is obtained from the nuclear modification factor, Rcp, in Au+Au collisions, which shows that there is a different pT dependence of hadron suppression in central collisions for baryons and mesons, consistent with quark coalescence. Evidence for a similar baryon–meson difference is also found in d+Au collisions.

Based on the relaxation equations describing the chemical equilibration of gluons, quarks and s quarks at finite baryon density derived from the Juttner distribution of partons, with the help of a rapid phase transition scenario from quark phase to hadron phase, we calculate strangeness production in the quark phase and hadron phase. It is found that the K−/π− ratio is enhanced to be larger than that in pp collisions by about a factor 3.

The production of strange particles in a hot medium as produced in collisions of heavy ions is considered one of the most important signals for the phase transition to a quark-gluon plasma. In the first part of this lecture, the theoretical description of strangeness production in hot matter is outlined for a gas of quarks and gluons and for a hadronic gas and its impact on the deconfinement phase transition. Then in the second part, constraints from the underlying chiral symmetry of Quantum Chromodynamics (QCD) are utilized to extract signals with strangeness for the chiral phase transition in hot matter., Comment: 22 pages, 9 figures, to be published as topical review for Journal of Physics G

I review the physics of strongly interacting matter at high (and not so high) baryon densities, as probed in nuclear collisions. Recent lattice results on the critical end point and the possibility to find it in experiment by searching for event-by-event fluctuations are discussed. Furthermore, I summarize the theoretical ideas on the in-medium properties of hadrons at non-zero baryon densities, in particular for kaons, D mesons and light vector mesons. Finally, I briefly discuss the role of baryon density for strangeness production in heavy-ion collisions and the possibility to obtain experimental information on hadron properties in cold nuclear matter from hadronic and electromagnetic reactions on nuclei.

Pion production, strangeness production and baryon stopping in elementary and nuclear collisions are discussed. It is argued that particle production in A+A reactions is closely related to that observed in p+p and p+A collisions. New features of baryon and anti-baryon production are pointed out. This leads to further conclusions about the similarities between p+p, p+A and A+A interactions.

We study the strangeness of a chemically equilibrating quark–gluon plasma at finite baryon density based on the Juttner distribution of partons. We find that the strangeness production depends obviously on the initial values, and will accelerate with the change of the initial system from a chemically non-equilibrated to an equilibrated system. We also find that the calculated strangeness is very different from the one in the thermodynamic equilibrium system. This study may be helpful to understand the formation of quark–gluon plasma via a chemically non-equilibrated evolution framework.

I will review the latest strangeness result measured in fixed target heavy-ion collisions at SIS, AGS and SPS before describing the first round of RHIC results. I will show that the systematic studies performed at the lower energies give a very consistent picture of enhanced strangeness production at SPS energies and hints of medium modification effects at the lower energies, which are dominated by larger baryon densities. The RHIC results complement this picture by again indicating strangeness production from a thermally equilibrated source, albeit at slightly higher freeze-out temperatures and lower baryon densities. RHIC adds significant new physics results to the field, though, by enabling the measurement of strange particle production at high transverse momentum, presently out to about 6 GeV/c. The new regime between 2 and 6 GeV/c is dominated by an interplay between traditional soft particle production, which is well described by hydrodynamical and thermal models, and production of strangeness from jet fragmentation. Potential new QGP signatures, such as jet quenching and elliptic flow due to parton collectivity, can be probed by measuring particle identified strange particle spectra out to high pt. I will review the latest results and show that these measurements breathe new life into a well-established field.

We review recent developments in the field of microscopic transport model calculations for ultrarelativistic heavy ion collisions. In particular, we focus on the strangeness production, for example, the phi-meson and its role as a messenger of the early phase of the system evolution. Moreover, we discuss the important effects of the (soft) field properties on the multiparticle system. We outline some current problems of the models as well as possible solutions to them., Comment: Invited talk at the 7th International Conference on Strangeness in Quark Matter, SQM 2003, Atlantic Beach, North Carolina, USA, 12-17 Mar, 2003. 11 pages, 12 figures

Recent results on p+p and p+A interactions are reviewed. They suggest that multiple collisions of the projectile in p+A reactions result in a non-trivial enhancement of strangeness production. This enhancement appears comparable to that observed in A+A interactions. The problem of isospin differences between proton and neutron projectiles is addressed. The question of separation between projectile and target is discussed. The importance of baryon stopping effects is indicated.

Some of the latest results of the PHOBOS experiment from the √s NN = 200 GeV Au+Au data are discussed. Those relevant to strangeness production are emphasized. These observations relate to the nature of the matter created when heavy ions collide at the highest achieved energy. The invariant yields of strange and non-strange charged hadrons at very low transverse momentum have been measured, and used to differentiate between different dynamical scenarios. In the intermediate transverse momentum range, the measured ratios of strange and anti-strange kaons approach one, while the antibaryon to baryon ratio is still significantly less, independent of collision centrality and transverse momentum. At high transverse momenta, we find that central and peripheral Au+Au collisions produce similar numbers of charged hadrons per participant nucleon pair, rather than per binary nucleon-nucleon collision.

We study the evolution of matter produced after the collision of two heavy nuclei at high energy. The matter produced may pass from the hadron phase into a new state of matter called quark–gluon plasma (QGP). The aim of this paper is to discuss how a new state of matter can be observed. Whilst matter is in the QGP phase, particles that arise from the interactions between the constituents of the plasma provide information concerning the state of the plasma.

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., Talk at "Strange Quarks in Matter" Conference (Strangeness'2001), September 2001, Frankfurt a.M., Germany

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 production of K+ and K- mesons in elementary proton-proton collision has been investigated at the Cooler Synchrotron COSY in Juelich. A high quality proton beam with low emittance and small momentum spread permitted to study 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 to study the interaction of the outgoing particles. Results on the performed studies of the pp --> pp K+ K-, pp --> p Lambda K+ and pp --> p Sigma0 K+ reactions will be presented and their relevance to the interpretation of heavy ion collisions will be discussed., 8 pages, 6 figures, plenary talk at 6th International Conference On Strange Quarks in Matter: '2001 - A Flavorspace Odyssey' (SQM2001), Frankfurt, Germany, September 25-29, 2001, to be published in J. Phys. G: Nucl. Part. Phys

The experiment NA50 studies the strangeness production by means of the BRμμσ/(BRρμμσρ + BRωμμσω) 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 BRμμσ/(BRρμμσρ + BRωμμσω) ratio shows an increase with the number of participants, in agreement with previous results. The inverse slope parameter extracted from the MT universal scaling is also studied.

Heavy ion collisions at SIS energies (1-2 AGeV) offer an 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 AGeV. Results on K0 production in Ru+Ru collisions at 1.69 AGeV are presented, as well as K-/K+ ratio as a function of rapidity. In addition, the sideward flow of charged and neutral strange particles has been measured. Results are compared to predictions of transport calculations (BUU and IQMD)., 8 pages, 6 figures, talk presented at SQM2001 in Frankfurt, Sept.2001, submitted to Journal of Physics G

The STAR detector has made a variety of measurements of strange and other hadronic species in Au+Au collisions at s N N = 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 indicator of the nuclear equation of state, the excitation function of the $K^+/\pi^+$ ratio and strangeness as a deconfinement indicator., Comment: 10 pages, 13 figures, invited talk at SQM2001, to appear in J. Phys. G

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.

Due to the absence of clear and unambiguous theoretical signals of the deconfinement transition from hadron matter to quark-gluon plasma (QGP) the experimental searches of QGP formation are based the analysis of various irregularities in the collision energy dependence of thermodynamic and hydrodynamic quantities. Here we present several remarkable irregularities at chemical freeze-out (CFO) of hadrons which are found using an advanced version of the hadron resonance gas model (HRGM). Among them are the sharp peaks of the trace anomaly and baryonic density which are seen at the center of mass energies √sNN = 4.9 GeV and √sNN = 9.2 GeV, and the two sets of highly correlated quasi-plateaus in the collision energy dependence of the entropy per baryon, total pion number per baryon, and thermal pion number per baryon which we found at the center of mass energies 3.8-4.9 GeV and 7.6-10 GeV. In addition we found a significant change of slope of the hadron yield ratios and , when the center of mass collision energy increases from 4.3 GeV to 4.9 GeV and from 7.6 GeV to 9.2 GeV [1]. The increase of slopes of these ratios at the collision energy interval 4.3-4.9 GeV is accompanied by a dramatic growth of resonance decays at CFO. We argue that such a strong correlation between the previously found irregularities and an enhancement of strangeness production can serve as the quark-gluon plasma formation signature. Hence, we conclude that a dramatic change of the system properties seen in the narrow collision energy range √sNN = 4.3-4.9 GeV may open entirely new possibilities for experimental studies of QGP properties at NICA JINR and FAIR GSI accelerators.

We present recent results on the sub-threshold production of strange and charmed hadrons in nuclear collisions. In particular we highlight how the excitation and decay of heavy baryonic resonances can be used to describe the production yield of mesons at the SIS18 accelerator and show how this production mechanism also consistently describes the nuclear transparency ratio. Including even more massive baryonic resonances in the model we are able to extend our approach and make, for the first time, realistic predictions on the sub-threshold production of J/Ψ and Λ c in nuclear collisions at the SIS100 accelerator at FAIR. We find that even at a beam energy of E lab = 6 A GeV, charm physics is feasible at the CBM experiment, which opens up new opportunities to study charmed hadron properties at large baryon densities.

Relativistic heavy ion collision is a fascinating field of research. In recent years, the field has seen an unprecedented level of progress. A new state of matter, deconfined quark–gluon plasma (QGP), was predicted. An accelerator was built to detect this new state of matter. Experiments were performed and the discovery of the 'most perfect fluid' was made. Conclusive identification of the most perfect fluid state with the deconfined state has yet to be achieved. One of the impediments towards such identification is the fundamental property of the strong interaction, the 'color confinement', i.e. the constituents of the theory, the 'colored' quarks and gluons, are confined within a hadron. Any information about the deconfined state must be amassed from the color-neutral hadrons. And yet the process by which colored building blocks convert into a color singlet state is not properly understood. This necessitates model building. To young researchers, the field poses a problem in that it is multi-disciplinary, requiring knowledge of thermodynamics, statistical physics, kinetic theory, group theory, quantum chromodynamics (QCD), etc. The complexity of heavy ion collisions has necessarily led to a proliferation of models, e.g. the thermal model, blast wave model hydrodynamic model and models based on transport equations, etc, the physics of which need to be understood.

This contribution summarizes the presentations and discussions concerning the experimental results from CERN SPS at the conference `Strangeness in Quark Matter', Berkeley, CA, 2000.

Strangeness and charm production will be the subject of intense experimental studies at RHIC. In this paper I discuss what is known at present about the strangeness and charm contents of the vacuum and light hadrons, and what can be expected in high-energy nuclear collisions. Some ideas for new measurements at RHIC are also presented.

The early summer of 2000 saw the start of the RHIC experimental programme. The PHOBOS collaboration used data from the beginning of the running period to extract the first physics information about this exciting new regime. This first measurement consisted of pseudorapidity densities of primary charged particles near mid-rapidity in central Au + Au collisions at beam energies which gave centre-of-mass energies per pair of colliding nucleons of √snn = 56 and 130 GeV. The observed densities are higher than those observed previously in any collisions in the laboratory. In addition, the rate of increase in density between the two energies is significantly larger than that for nucleon-nucleon collisions at comparable beam energies. This paper will briefly describe the PHOBOS experiment (including the subset of the full detector installed for the early period of the RHIC beam), discuss the results of the first physics measurement and conclude with the prospects for the future, especially in the area of strangeness production.

The present status of experimental results on strange particle production in Pb + Pb collisions at the CERN-SPS is reviewed. The paper presents a comparison of multiplicities, rapidity distributions and transverse mass spectra for central collisions measured by different experiments and a discussion of the centrality dependence of strangeness production.

The RHIC era in relativistic heavy-ion collisions promises to be an exciting time of experimental revelation of the properties of high-temperature quantum chromodynamics and the quark-gluon plasma. In this paper I will introduce the PHENIX experiment's capabilities and physics goals, and discuss in particular measurements of strangeness production that will be made by the PHENIX collaboration as part of a comprehensive physics programme.