We present an overview of recent STAR results on strangeness production in p+p and heavy-ion collisions at RHIC. In both Cu+Cu and Au+Au collisions we show the centrality dependencies of bulk yield and mid-$p_{T}$ spectrum measurements with new comparisons to theory. The latest $v_{2}$ results for strange particles are presented and prospects for strangeness production in the low energy scan program will be outlined. Finally, we report new measurements of strangeness fragmentation functions for jets in p+p collisions.
In this paper I highlight a few selected topics on strange particle production in heavy-ion collisions. By studying the yield and spectra of strange particles we hope to gain understanding of the conditions reached in, and the ensuing dynamics of, the systems produced when ultra-relativistic heavy-ions are collided.
STAR is a large acceptance spectrometer capable of precision measurements of a wide variety of strange particles. We discuss the STAR detector, its configuration during the first two years of RHIC operation, and its initial performance for Au+Au collisions. The expected performance for strangeness physics and initial data on strange particle reconstruction in Au+Au collisions are presented.
Selected topics in Strangeness Nuclear Physics are reviewed: Lambda-hypernuclear spectroscopy and structure, Sigma-hyperon nuclear interaction, multistrangeness, and anti-kaons in nuclei.
Open questions concerning strangeness production in heavy-ion collisions are discussed with a focus on the experimental aspects. The open points are presented in the context of recent measurements.
The paper gives an overview of strangeness-production experiments at the Cooler Synchrotron COSY. Results on kaon-pair and phi meson production in pp, pd and dd collisions, hyperon-production experiments and Lambda p final-state interaction studies are presented.
n this paper we review the recent results on strangeness production measured by HADES in the Ar+KCl system at a beam energy of 1.756 AGeV. A detailed comparison of the measured hadron yields with the statistical model is also discussed.
The role of Strangeness as a signal of the Quark Gluon Plasma in relativistic heavy ion experiments is discussed. The current experimental status is briefly presented. Several scenarios which explain the CERN data are discussed.
Experimental results for photo- and electro-production of open strangeness from the Thomas Jefferson National Accelerator Facility are discussed. The results are from work completed by mid-2003 on elementary $KY$ production, nuclear targets, and the exotic $Θ^+$ state. It is shown how the increases in intensity and precision of JLab experiments over earlier work have allowed new phenomena to become measurable.
Strangeness measurement at RHIC energies constitutes one of the favorite theme of the STAR Collaboration. Besides the fact that strangeness enhancement has been proposed as a quark gluon plasma signature, its production provides various and relevant information about the collision evolution and especially on the hadronization process. The investigation of short-lived strange particles as well as their anti-particles and resonances allows an attempt of characterization of the matter created in RHIC heavy ion collisions.
Published measurements of semi-inclusive Lambda production in p-Au collisions at the AGS are used to estimate the yields of singly strange hadrons in nucleus-nucleus A-A collisions. Results of a described extrapolation technique are shown and compared to measurements of K+ production in Si-Al, Si-Au, and Au-Au collisions at the AGS and net Lambda production in Su-Su, S-Ag, Pb-Pb, and inclusive p-A collisions at the SPS. The extrapolations can account for more than 75% of the measured strange particle yields in all of the studied systems except for very central Au-Au collisions at the AGS where…
Strangeness production in Au+Au collisions has been measured via the yields of K+ and K- at 6, 8 AGeV and of anti-Lambda at 10.8 AGeV beam kinetic energy in experiment E917. By varying the collision centrality and beam energy, a systematic search for indications of new phenomena and in-medium effects under high baryon density is undertaken.
Strange particle production in A+A interactions at 158 AGeV is studied by the CERN experiment NA49 as a function of system size and collision geometry. Yields of charged kaons, phi and Lambda are measured and compared to those of pions in central C+C, Si+Si and centrality-selected Pb+Pb reactions. An overall increase of relative strangeness production with the size of the system is observed which does not scale with the number of participants. Arguing that rescattering of secondaries plays a minor role in small systems the observed strangeness enhancement can be related to the space-time densi…
In order to understand strangeness production mechanisms, one can study the correlations of hadrons with hidden strangeness (e.g. the $ϕ$ meson) and open strangeness ($\mathrm{K}^{0}_{\mathrm{S}}$, $Λ$ and $\barΛ$) in hard (jet) processes and in soft (bulk) processes. Two-particle angular correlations with $\mathrm{K}^{0}_{\mathrm{S}}$ triggers allow for the study of fragmentation in pp collisions as a function of multiplicity. Similarly, correlations with associated $ϕ$ mesons in p-Pb collisions allow both the jet and the underlying event components of strange particle production to be probed…
We present a summary of strange particle yields measured by the experiment NA49 in central Pb+Pb collisions in the beam energy range 20-158 AGeV. The comparison with thermal hadron model results shows that above 30 AGeV, a strangeness undersaturation parameter gamma_S must be employed to describe the data. This suggests a change in the strangeness production mechanism at this energy. We find that the UrQMD transport model in all cases underpredicts the observed particle yields.
We present a summary of strangeness enhancement results comparing data from Cu+Cu and Au+Au collisions at sqrt(SNN) = 200GeV measured by the STAR experiment. Relative yields in central Cu+Cu data seem to be higher than the equivalent sized peripheral Au+Au collision. In addition, strange particle production from these two systems is compared in terms of a statistical model, applying a Grand-Canonical ensemble and also applying a canonical correlation volume for the strange particles. Thermal fit results from the Grand-Canonical formalism shows little dependence on the system size but, when con…
Emission of pi, K, phi and Lambda was measured in near-central C+C and Si+Si collisions at 158 AGeV beam energy. Together with earlier data for p+p, S+S and Pb+Pb, the system-size dependence of relative strangeness production in nucleus-nucleus collisions is obtained. Its fast rise and the saturation observed at about 60 participating nucleons can be understood as onset of the formation of coherent partonic subsystems of increasing size.
Strangeness study is one of the major goal of the STAR experiment at RHIC. Results presented here have been obtained from analyses restricted to the mid-rapidity region of Au-Au collisions at $\sqrt{s_{NN}}$ = 130 GeV. An onset of the understanding of the quark matter behavior produced at this relativistic energy can be stressed from the investigation of the relative and absolute yields of strange particle production, their transverse mass distributions and from comparisons with previous results obtained by AGS and SPS experiments.
Measurements of strangeness production in jets help illuminate the QCD mechanisms in fragmentation. Furthermore, they provide a crucial baseline for heavy-ion studies where modifications in jet chemistry have recently been observed by the STAR experiment. We present new results on strange particle production in jets from p+p $\sqrt{s}$ = 200 GeV collisions measured by the STAR experiment. The fragmentation functions of the Λ, \barΛ and K0Short particles are obtained using various jet finding algorithms, and then compared to various models. Strange particle ratios in jets will be obtained and c…
A study of the yields of strange particles produced in heavy-ion and elementary collisions is presented using preliminary results from the STAR experiment at RHIC. The strange particle production rates, relative to those of p+p, have been proposed as a means of determining an enhancement of strangeness production in heavy-ion collisions. Analysis of results from STAR show that this enhancement measure is reduced, or comparable, when contrasted to that at top CERN SPS energies. A smaller suppression in the p+p yields at RHIC energies due to finite volume effects could be the cause of such a res…
We report recent results of strangeness and heavy flavor measurements from PHENIX. The topics are: Elliptic flow of strangeness and heavy flavor electron production comparing to the other hadrons, $ϕ$ meson production, and an exotic particle search.
Measurements of strangeness production in jets help illuminate the QCD mechanisms in fragmentation. Furthermore, they provide a crucial baseline for heavy-ion studies where modifications in jet chemistry have recently been predicted. We present new results on strange particle production in jets from p+p \sqrt{s} = 200 GeV collisions measured by the STAR experiment. The momentum distributions of the Λ, \barΛ and K0Short particles are obtained using various jet finding algorithms, and then compared to various models. Strange particle ratios in jets are obtained and compared to values obtained fr…
Due to its large acceptance, the STAR experiment has acquired a wealth of data on strangeness production for a variety of collisions systems and energies, from p+p to Au+Au. By using the yields and spectra, we address the evolution of the bulk system, including strangeness enhancement and the flavour dependence of radial and elliptic flow. Utilising the fact that we can identify strange baryons and mesons, we investigate different hadronization mechanisms in the intermediate and high p$_{T}$ regions. The ratios of the particle yields, measured to high p$_{T}$, are used to further investigate t…
Systematic studies on the production of strange hyperons and the phi meson as a function of beam energy and system size performed by the NA49 collaboration are discussed. Hadronic transport models fail to describe the production of multi strange particles (Xi, Omega), while statistical models are generally in good agreement to the measured particle yields at all energies. The system size dependence is well reproduced by the core-corona approach. New data on K*(892) production are presented. The yields of these short-lived resonances are significantly below the statistical model expectation. Th…
Preliminary results on strange particle production versus collision centrality are presented. STAR measurements from \sqrts = 200 GeV heavy-ion and \pp collisions are compared to SPS measurements. A systematic study of strange particle production is presented with the aim of establishing how the correlation volume of the produced source affects the scale of strange particle creation, including that of the multi-strange baryons. A linear increase of strangeness production with volume has been suggested by thermal models as an indication that the collision region has reached sufficient size such…
We report on the measurements of strange hadron ($K^0_S$, $Λ$, $Ξ$) production in the most central (0-20%) d+Au collisions at \sqrt{s_{NN}} = 200 GeV in STAR. Significant strangeness enhancement is observed in the most central d+Au collisions, especially for multi-strange hyperons ($Ξ$). The nuclear modification factor ($R_{dAu}$) of identified particles shows possible particle type -- baryon (protons, $Λ$), meson ($π$,$K^0_S$, $ϕ$) -- dependence at intermediate $p_T$ (2 - 3.5 GeV/c), indicating that the final state may have an impact on the Cronin effect.
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.
The paper provides a short report on strangeness production in ultrarelativistic nucleus-nucleus collision, with the main stress on strange particle abundances.
Strangeness production in heavy-ion collisions, when compared to proton proton collisions, is potentially a sensitive probe for collective energy deposition and therefore for reaction mechanisms in general. It may therefore provide insight into possible QGP formation in dense nuclear matter. To establish an understanding of the observed yields, a systematic study of high density baryon matter at different beam energies is essential. This might also reveal possible discontinuities in the energy dependence of the reaction mechanism. We present preliminary results for kaon production in Au+Au col…
We report an overview of strangeness production in Cu+Cu and Au+Au collisions at the energies $\sqrt{s_{NN}} =$ 62.4 and 200 GeV. We show new mid-rapidly $dN/dy$ results for the $K^{0}_{S}$, $Λ$, $Ξ$, $Ω$ particles in Cu+Cu \sNN{62} collisions and compare to results in Au+Au \sNN{62} collisions. We show new results for mid-$p_T$ $Λ/K^{0}_{S}$ ratios in Cu+Cu \sNN{62} collisions and again compare to ratios in Au+Au \sNN{62} collisions. Finally, we show the high-$p_{T}$ ($\sim 6.2$ GeV/c) $R_{AA}(K^{0}_{S})$ as a function of system size in Au+Au \sNN{200} collisions and compare to $R_{AA}(π)$.
We present a model of exclusive $ϕ$-meson lepto-production $ep \to e'p'ϕ$ near threshold which features the strangeness gravitational form factors of the proton. We argue that the shape of the differential cross section $dσ/dt$ is a sensitive probe of the strangeness D-term of the proton.
Resent results concerning the production of K+, K-, phi, K0 S and lambda particles in the reaction system Ar+KCl at 1.76 AGeV measured by the HADES Collaboration are presented. Transverse momentum distributions have been measured in a large fraction of the phase space. For the first time, at SIS energies, K+, K- and phi mesons have been measured independently and the slope parameter for phi mesons could be extracted. A large statistics has been collected for the produced K0S and lambda in the phase space region around mid-rapity. The high quality of these data render them very suitable for com…
We present a summary of measurements of strange particles performed by the experiment NA49 in inelastic p+p interactions, as well as semi-central C+C and Si+Si, central Pb+Pb, and minimum bias Pb+Pb collisions in the energy range $\sqrt{s_{NN}}$ = 6.3 - 17.3 GeV. New results on $π^{-}$, $K^{+}$ and $K^{-}$ production in minimum bias Pb+Pb collisions at $\sqrt{s_{NN}}$ = 8.7 and 17.3 are shown. Furthermore the strangeness enhancement factor at $\sqrt{s_{NN}}$ = 17.3 GeV is presented and compared to the results from NA57 and STAR. Energy dependence of strange particle yields normalized to pion y…
We present measurements of strange and multi-strange hadrons in p+p collisions at $\sqrt{s}$= 200 GeV measured by STAR. We will compare these preliminary results to leading-order (LO) and next-to-leading order (NLO) perturbative QCD models widely believed to describe the production mechanisms. In particular we will point out recent changes of the model calculations which improve the agreement with our data significantly and will discuss the physics consequences. In larger collision systems, produced with heavy ions at RHIC, we observe the centrality dependence of strange and multi-strange part…
The yields and spectra of strange hadrons have each been measured by STAR as a function of centrality in $\rm \sqrt{s_{NN}}=$ 200 GeV AuAu collisions. By comparison to measurements in pp and dAu at $\rm \sqrt{s_{NN}}=200$ GeV and in AuAu at $\rm \sqrt{s_{NN}}=62$ GeV the dependence on system size and energy is studied. Short-lived resonances, such as $Σ(1385)$ and $Λ(1520)$, that may decay and regenerate in the medium, are used to examine the dynamical evolution between production and freeze-out for these systems. Particle production is investigated by comparison to thermal models, which assum…
Identified charged kaon, pion, and proton spectra and ratios from sqrt(s_NN) = 200 and 62.4 GeV Cu+Cu collisions are studied with a hydro-motivated blast-wave and a statistical model framework in order to explore the strangeness production at RHIC and characterize the bulk freeze-out properties of the created system. The spectra are measured at mid-rapidity |y|<0.1 over the transverse momentum range of 0.25 < p_T < 1.2 GeV/c with particle identification derived from the ionization energy loss in the STAR Time Projection Chamber. The multi-dimensional systematic study of pi(+/-), K(+/-), p and …
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…
Associated strangeness production close to threshold is a particularly clean example of how energy is converted into hadronic matter. Final results from the completed experiments of the PS185 collaboration at LEAR/CERN, using the antiproton-proton interaction to produce antihyperon-hyperon pairs, demonstrate that such studies form a powerful tool. First results from the ongoing investigations of the COSY-11 collaboration at COSY-J"ulich, measuring the strangeness dissociation into both hyperon-kaon and kaon-kaon pairs from proton-proton scattering, are presented and plans for further investiga…
In these proceedings, two multi-differential analyses performed in pp collisions collected by the ALICE collaboration during the LHC Run 2 are presented. One investigates the dependence of strange particle production with multiplicity and effective energy, whereas the other clarifies how strangeness enhancement is correlated to the leading jet in the event. The results suggest that strangeness production at the LHC depends strongly on effective energy, and originates dominantly from the transverse region with respect to the leading jet direction.
The paper gives an overview of strangeness-production experiments at the Cooler Synchrotron COSY. Results on kaon-pair and $ϕ$ meson production in $pp$, $pd$ and $dd$ collisions, hyperon-production experiments and $Λp$ final-state interaction studies are presented as well as a search for a strangeness $S=-1$ resonance in the $Λp$ system.
Strangeness production has long been proposed as a diagnostic tool for understanding the dynamics of relativistic heavy ion collisions. In this presentation we review the traditional picture of strangeness enhancement as a signature for quark-gluon plasma formation. We then review, in order, some experimental data on strange particle production in $e^{+}e^{-}$, $pp$, $p\bar{p}$, proton-nucleus and nucleus-nucleus collisions. This is not a comprehensive review, but rather an emphasis of a few significant points. Any clear interpretation of strange particle yields measured in heavy ion reactions…
Double strangeness $Ξ^{-}$ production in Au+Au collisions at 2, 4, and 6 GeV/nucleon incident beam energies is studied with the pure hadron cascade version of a multi-phase transport model. It is found that due to larger nuclear compression, the model with the soft equation of state (EoS) gives larger yields of both single strangeness ($K^{+}$ and $Λ+Σ^{0}$) and double strangeness $Ξ^{-}$. The sensitivity of the double strangeness $Ξ^{-}$ to the EoS is evidently larger than that of $K^{+}$ or $Λ+Σ^{0}$ since the phase-space distribution of produced $Ξ^{-}$ is more compact compared to those of …
The COoler SYnchrotron COSY-Jülich delivers phase-space cooled, polarized proton and deuteron beams with momenta up to p=3.65 GeV/c. Various experiments on hadron-induced strangeness production on proton, neutron and nuclear targets have been carried out. Here we report about recent results on associated strangeness production in pp -> KYN (Y= Lambda,Sigma) reactions, on K^+ production in pn collisions, and on K K-bar pair production in pp interactions. We also briefly discuss possible measurements to disentangle the parity of the recently discovered pentaquark state Theta^+, the spin dependen…
Hadronic resonances are unique tools to investigate the interplay of re-scattering and regeneration effects in the hadronic phase of heavy-ion collisions. As the $ϕ$ meson has a longer lifetime compared to other resonances, it is expected that its production will not be affected by regeneration and re-scattering processes. Measurements in small collision systems such as proton-proton (pp) collisions provide a necessary baseline for heavy-ion data and help to tune pQCD inspired event generators. Given that the $ϕ$ is a bound state of strange-antistrange quark pair (s$\bar{\rm{s}}$), measurement…
We present an analysis of data on light flavour hadron production as function of event multiplicity at LHC energies measured by the ALICE collaboration. The strangeness-canonical approach within the framework of the THERMUS statistical hadronisation model is used for a simultaneous description of pp, p-Pb, and Pb-Pb collisions. The rapidity window dependence of the strangeness correlation volume is addressed and a value of $Δy = 1.33 \pm 0.28$ is found. With the exception of the $ϕ$-meson, an excellent description of the experimental data is found.
We review the experimental results on strangeness and antibaryon production in heavy-ion collisions at the AGS and SPS. We argue that the observed enhancement in kaon production at the AGS is consistent with hadronic description, while the multistrange baryon and antibaryon results at the SPS may need physics beyond hadronic nature. We call the need for measurements of low energy antilambda-proton annihilation cross-section in the modeling of antilambda to antiproton ratio; large value of this ratio is observed in central heavy-ion collisions at the AGS and SPS. We speculate the importance of …
An experimental overview of the energy dependence of strangeness production is presented. The strange hadrons are considered a good probe to study the QCD matter created in relativistic nucleus-nucleus collisions. The heavy-ion experiments at SPS, RHIC, and LHC have recorded a wealth of data in proton-proton, proton-nucleus and nucleus-nucleus collisions at several beam energies. In this proceeding, I discuss the invariant yield and azimuthal anisotropy measurement of strange hadrons in nucleus-nucleus collisions at SPS, RHIC, and LHC.
This article summarises the highlights of the recent experimental findings on strangeness production presented at the 16th edition of the {\it International Conference on Strangeness in Quark Matter} in Berkeley. Results obtained by eight large experimental collaborations (ALICE, ATLAS, CMS, HADES, LHCb, NA-61, PHENIX, STAR) spanning a large range in centre-of-mass energy and a variety of collision systems were presented at the conference. The article does not aim at being a complete review, but rather at connecting the experimental highlights of the different collaborations and at pointing to…
The study of energy and multiplicity dependence of strange hadron production in proton-proton collisions provides a powerful tool to understand similarities and differences between small and large collision systems. In order to better understand the origin of strangeness enhancement in pp new multi-differential analyses have been performed. The first separates the contribution of soft and hard processes, such as jets, to strange hadron production through two-particle correlation techniques. The second exploits the concept of the effective energy available for particle production in the event, …
The main goal of the ALICE experiment is to study the properties of the hot and dense medium created in ultra-relativistic heavy-ion collisions. The measurement of the (multi-)strange particles is an important tool to understand particle production mechanisms and the dynamics of the quark-gluon plasma (QGP). We report on the production of K$^{0}_{S}$, $Λ$($\overlineΛ$), $Ξ^{-}$($\overlineΞ^{+}$) and $Ω^{-}$($\overlineΩ^{+}$) in proton-lead (p-Pb) collisions at $\sqrt{s_{\rm NN}}$ = 5.02 TeV and lead-lead (Pb-Pb) collisions at $\sqrt{s_{\rm NN}}$ = 2.76 TeV measured by ALICE at the LHC. The com…
New experimental data on transverse momentum spectra of strange particles (KS0, K-, K*, phi,...) produced in pp collisions at sqrt s = 200 GeV obtained by the STAR and PHENIX collaborations at RHIC are analysed in the framework of z-scaling approach. Scaling properties of the data z-presentation are illustrated. Self-similarity of strange particle production is discussed. A microscopic scenario of constituent interactions developed within the z-scaling approach is used to study constituent energy loss, proton momentum fraction and recoil mass in dependence on the transverse momentum, strangene…
The ALICE experiment has studied strangeness production in different collision systems (pp, p-Pb, Xe-Xe and Pb-Pb) and energies. The ratio of the strange particle yield to pion yield as a function of multiplicity for different collision energies and systems follow a continuously increasing trend ("enhancement") from low multiplicity pp to high-multiplicity Pb-Pb collisions, independent of the initial collision energy and colliding particles. It is also observed that the enhancement is larger for the particles with larger strangeness content. Several other features that were observed in large c…
Recent measurements performed in high-multiplicity proton-proton (pp) and proton-lead (p-Pb) collisions have shown features that are reminiscent of those observed in lead-lead (Pb-Pb) collisions. These observations warrant a comprehensive measurement of the production of identified particles. We report on the production of \allparts at mid-rapidity measured as a function of multiplicity in pp collisions at $\sqrt{s}$ = 7 TeV with the ALICE experiment. Spectral shapes studied both for individual particles and via particle ratios such as ($Λ/K^{0}_{S}$) as a function of $p_{T}$ exhibit an evolut…
The results of the microscopic transport calculations of $\bar p$-nucleus interactions within a GiBUU model are presented. The dominating mechanism of hyperon production is the strangeness exchange processes $\bar K N \to Y π$ and $\bar K N \to ΞK$. The calculated rapidity spectra of $Ξ$ hyperons are significantly shifted to forward rapidities with respect to the spectra of $S=-1$ hyperons. We argue that this shift should be a sensitive test for the possible exotic mechanisms of $\bar p$-nucleus annihilation. The production of the double $Λ$-hypernuclei by $Ξ^-$ interaction with a secondary ta…
The capabilities of the new version of the Liège Intra-Nuclear Cascade model (INCL++6) are presented in detail. This new version INCL is able to handle strange particles, such as kaons and the $Λ$ particle, and the associated reactions and also allows extending nucleon-nucleon collisions up to about $15-20$ GeV incident energy. Compared to the previous version, new observables can be studied, e.g., kaon, hyperon, and hypernuclei production cross sections (with the use of a suitable de-excitation code) as well as aspects of kaon-induced spallation reactions. The main purpose of this paper is to…
We present an overview of a fully covariant formulation for describing the production of strangeness -1 and -2 hypernuclei using probes of different kinds. This theory is based on an effective Lagrangian picture and it focuses on production amplitudes that are described via creation, propagation and decay into relevant channel of intermediate baryonic resonance states in the initial collision of the projectile with one of the target nucleons. The bound state nucleon and hyperon wave functions are obtained by solving the Dirac equation with appropriate scalar and vector potentials. Specific exa…
One of the key results of the LHC Run 1 was the observation of an enhanced production of strange particles in high multiplicity pp and p--Pb collisions at $\sqrt{s_\mathrm{NN}}$ = 7 and 5.02 TeV, respectively. The strangeness enhancement is investigated by measuring the evolution with multiplicity of single-strange and multi-strange baryon production relative to non-strange particles. A smooth increase of strange particle yields relative to the non-strange ones with event multiplicity has been observed in such systems. We report the latest results on multiplicity dependence of strange and mult…
