The properties of strange pseudoscalar and vectors mesons as well as strange baryon resonances in dense matter are reviewed. Some open questions on the properties of strange hadrons in medium are addressed, such as the experimental signatures of in-medium effects coming from the hadronic phase on the final observables in heavy-ion collisions for the experimental conditions at SIS, RHIC and LHC energies.
The parton and hadron cascade model PACIAE based on PYTHIA was utilized to systematically investigate the strange particle production in pp collisions at the RHIC and LHC energies. Taking the mechanism of reduction of the strange quark suppression into account the STAR and ALICE data of strange particle production in pp collisions are well reproduced. It turned out that the K/π ratio as a function of reaction energy in pp collisions shows slightly increasing from sqrt(s)=0.2 to 0.9 TeV and then turning to saturation.
We study, in the dynamically evolving QGP fireball formed in relativistic heavy ion collisions at RHIC and LHC, the growth of strangeness yield toward and beyond the chemical equilibrium. We account for the contribution of the direct strangeness production and evaluate the thermal-QCD strangeness production mechanisms. The specific yield of strangeness per entropy, s/S, is the primary target variable. We explore the effect of collision impact parameter, i.e., fireball size, on kinetic strangeness chemical equilibration in QGP. Insights gained in study the RHIC data with regard to the dynamics …
We determine chemical freeze-out conditions from strangeness observables measured at RHIC beam energies. Based on a combined analysis of lowest-order net-Kaon fluctuations and strange anti-baryon over baryon yield ratios we obtain visibly enhanced freeze-out conditions at high beam energies compared to previous studies which analyzed net-proton and net-charge fluctuations. Our findings are in qualitative agreement with the recent study [1] which utilizes the net-Kaon fluctuation data in combination with information from lattice QCD. Our complimentary approach shows that also strange hadron yie…
The parton and hadron cascade model PACIAE is used to investigate strange particle production in Au + Au collisions at GeV in different centralities and at 39, 11.5 and 7.7 GeV in the most central collision, respectively. It is shown that the transverse momentum distributions of strange particles by the PACIAE model fit the RHIC Beam Energy Scan experimental results well.
PACIAE, a parton and hadron cascade model, is utilized to systematically investigate strange particle production and strangeness enhancement in Au+Au collision and in Pb+Pb collision with the 200GeV at RHIC and 2.76TeV at LHC, respectively. The experimental results at different centrality, which come from the STAR collaboration and the ALICE collaboration, are well described by the PACIAE model. This may represent the importance of the parton and hadron rescatterings, as well as the reduction mechanism of strange quark suppression, added in the PACIAE model.
Strange particle ratios and pT-spectra are calculated in a thermal model with single freeze-out, previously used successfully to describe non-strange particle production at RHIC. The model and the recently released data for phi, Lambda, anti-Lambda, and K*(892) are in very satisfactory agreement, showing that the thermal approach can be used to describe the strangeness production at RHIC.
We have estimated centrality variation of chemical freeze-out parameters from yield data at mid-rapidity of $π^\pm$, $K^\pm$ and $p$, $\bar{p}$ for collision energies of RHIC (Relativistic Heavy Ion Collider), Beam Energy Scan (RHIC-BES) program, and LHC (Large Hadron Collider). We have considered a simple hadron resonance gas model and employed a formalism involving conserved charges ($B, Q, S$) of QCD for parameterization. Along with temperature and three chemical potentials ($T,μ_B,μ_Q,μ_S$), a strangeness under-saturation factor ($γ_S$) has been used to incorporate the partial equilibratio…
We systematically compare an event-by-event transport+viscous hydrodynamics hybrid model to data from the RHIC beam energy scan using a general Bayesian method. We demonstrate how the inclusion of multistrange hadron observables affects the outcome of the Bayesian analysis and conduct an in depth analysis of the viability of $ϕ$ and $Ω$ as probes of the transition region between a deconfined quark-gluon plasma and hadronic phase in heavy ion collisions at higher-end RHIC collision energies. Utilizing UrQMD to model the final hadronic interactions, we examine the collision rates of $ϕ$ and $Ω$ …
Using the moments of the net-kaon distribution calculated within a state of-the-art hadron resonance gas model compared to experimental data from STAR's Beam Energy Scan, we find that the extracted strange freeze-out temperature is incompatible with the light one extracted from net-proton and net-charge fluctuations. Additionally predictions for net-$Lambda$ fluctuations are made that also appear to be consistent with a higher freeze-out temperature for strange particles. This strangeness freeze-out temperature is roughly $10-15$ MeV higher than the corresponding light freeze-out temperature. …
We study e+e- pair production in proton-proton and in nucleus-nucleus collisions from SIS to LHC energies within the parton-hadron-string dynamics (PHSD) approach which incorporates explicit partonic degrees-of-freedom in terms of strongly interacting quasiparticles (quarks and gluons) in line with an equation-of-state from lattice QCD as well as the dynamical hadronization and hadronic collision dynamics in the final reaction phase. We find a visible in-medium effect in the low mass dilepton sector from dynamical vector-meson spectral functions from SIS to SPS energies whereas at RHIC and LHC…
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…
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. Here, the results of the 1-dimensional correlation analysis are presented. The extracted in…
The production and freeze-out conditions of strange particles, produced in Au+Au collisions at RHIC energies, are studied within microscopic transport model. The system of final particles can be represented as a core, containing the particles which are still interacting with each other, and a halo, in which the particles have already decoupled from the system. In microscopic calculations hadrons are continuously emitted from the whole reaction volume. At RHIC, however, significant fractions of both mesons and baryons are emitted from the surface region within the first two fm/c. Different spec…
Anisotropic flow of K's, anti-K's, and lambdas 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 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, $v_1^{K,\bar{K}, Λ}(y)$, have universal negative slope at $|y| \leq 2$ at RHIC. The e…
We review the current status of strangeness as signature of the formation and dissociation of the deconfined QGP at the SPS energy scale, and present the status of our considerations for RHIC energies. By analyzing, within the framework of a Fermi statistical model, the hadron abundance and spectra, the properties of a disintegrating, hadron evaporating, deconfined QGP fireball are determined and can be compared with theory for the energy range 160--200AGeV on fixed target. We discuss in more detail our finding that the pion yields occur near to pion condensation condition. Dynamical models of…
New results of analysis of $K^0_S-$meson spectra measured over a wide range of energy $\sqrt {s_{NN}}=7.7-200$ GeV and centrality in $Au+Au$ collisions by the STAR Collaboration at RHIC using the $z$-scaling approach are presented. Indication on self-similarity of fractal structure of nuclei and fragmentation processes with $K^0_S$ probe is demonstrated. The energy loss as a function of the collision energy, centrality and transverse momentum of the inclusive strange meson is estimated.
We apply a quark combination model to study yield densities and transverse momentum ($p_{T}$) spectra of strange (anti-)hadrons at mid-rapidity in central Au+Au collisions at $\sqrt{s_{NN}}=$ 7.7, 11.5, 19.6, 27, 39 and 200 GeV. We show that experimental data for $p_{T}$ spectra of (anti-)hadrons in these collisions can be systematically described by the equal velocity combination of constituent quarks and antiquarks at hadronization. We obtain $p_{T}$ spectra of quarks and antiquarks at hadronization and study their collision energy dependence. We also reproduce the yield densities of hadrons…
Two major aspects of strange particle physics at the upcoming FAIR and NICA facilities and the RHIC low energy scan will be discussed. A new distinct production mechanism for hypernuclei will be presented, namely the production abundances for hypernuclei from $Λ$'s absorbed in the spectator matter in peripheral heavy ion collisions. As strangeness is not uniformly distributed in the fireball of a heavy ion collision, the properties of the equation of state therefore depend on the local strangeness fraction. The same, inside neutron stars strangeness is not conserved and lattice studies on the …
We study effects of the hadronic rescattering on final observables especially for multi-strange hadrons such as $ϕ$, $Ξ$ and $Ω$ in high-energy heavy-ion collisions within an integrated dynamical approach. In this approach, (3+1)-dimensional ideal hydrodynamics is combined with a microscopic transport model, JAM. We simulate the collisions with or without hadronic rescatterings and compare observables between these two options so that we quantify the effects of the hadronic rescattering. We find that the mean transverse momentum and the elliptic flow parameter of multi-strange hadrons are less…
Based on A Multi-Phase Transport (AMPT) model, we have studied the elliptic flow $v_{2}$ of $ϕ$ mesons from reconstructed $K^{+}K^{-}$ decay channel at the top Relativistic Heavy Ion Collider energy at Brookhaven National Laboratory. The dependences of $v_{2}$ on transverse momentum $p_T$ and collision centrality are presented and the rescattering effect of $ϕ$ mesons in the hadronic phase is also investigated. The results show that experimental measurement of $v_{2}$ for $ϕ$ mesons can retain the early collision information before $ϕ$ decays and that the $ϕ$ $v_2$ value obeys the constituent …
Strangeness and baryon enhancement in heavy ion collisions are discussed in the framework of the String Fusion Model. The Monte Carlo version of this model is shown to reasonably reproduce three of the features that have been pointed out as evidences of the finding of the Quark Gluon Plasma. Namely hyperon/antihyperon enhancement, dependence of the slope of the $p_{T}$ distributions on the mass of the produced particles and on the centrality of the collision, are described. Predictions for RHIC and LHC energies are presented.
We calculate the inclusive production of a polarized $Λ$ or $\barΛ$ hyperon from the single longitudinally polarized proton and proton ($pp$) collision at RHIC. By comparing the data reported by the STAR Collaboration, we find that this process is sensitive to the polarization of strange and antistrange quarks of the proton in the experimental range. By introducing asymmetric coefficients with the minimization of $χ^2$, we further identify the asymmetry of the polarized strange-antistrange quarks in the proton sea and find that the first moment is $Δs \approx -0.025\pm 0.019$ for strange quark…
Space-time picture of the anisotropic flow evolution in Au+Au collisions at BNL RHIC is studied for strange hadrons within the microscopic quark-gluon string model. The directed flow of both mesons and hyperons demonstrates wiggle structure with the universal antiflow slope at |y| < 2 for minimum bias events. This effect increases as the reaction becomes more peripheral. The development of both components of the anisotropic flow is closely related to particle freeze-out. Hadrons are emitted continuously, and different hadronic species are decoupled from the system at different times. These had…
We attempt to describe the rapidity and transverse momentum spectra of strange as well as non-strange hadrons e.g. cascade,cascadebar, lambda , lambdabar, proton, protonbar,(omega+omegabar, Kaon, anti-Kaon and their ratios in the ultra-relativistic collisions of gold nuclei at (Root sNN)=200 GeV. This is done by using a statistical thermal freeze-out model which incorporates the rapidity (collision) axis as well as transverse direction boosts developed within an expanding hot and dense hadronic fluid (fireball) till the final freeze-out. We determine the thermo-chemical freeze-out conditions p…
The properties of $K$ and $\bar K$ mesons in nuclear matter at finite temperature are obtained from a chiral unitary approach in coupled channels which incorporates the $s$- and p-waves of the kaon-nucleon interaction. The in-medium solution accounts for Pauli blocking effects, mean-field binding on all the baryons involved, and $π$ and kaon self-energies. The $\bar K$ spectral function spreads over a wide range of energies, reflecting the melting of the $Λ(1405)$ resonance and the contribution of hyperon-hole components at finite temperature. In the $KN$ sector, the quasi-particle peak is con…
Strangeness production is calculated in a pQCD-based model (including nuclear effects) in the high transverse momentum sector, where pQCD is expected to work well. We investigate pion, kaon, proton and lambda production in pp and heavy-ion collisions. Parton energy loss in AA collisions is taken into account. We compare strange-to-non-strange meson and baryon ratios to data at RHIC, and make predictions for the LHC. We find that these ratios significantly deviate from unity not only at RHIC but also at the LHC, indicating the special role of strangeness at both energies.
Statistical hadronization is presented as mechanism for (strange) particle production from a deconfined quark--gluon plasma (QGP) fireball. We first consider hadronic resonance production at RHIC as a test of the model. We present in detail how the hadrochemistry determines particle multiplicities and in case of sudden hadronization allows investigation of QGP properties. A comparative study of strange hadron production at SPS and RHIC is presented. The energy dependence of physical observables shows regularities and a potential discontinuity in the low RHIC range, when comparing these differe…
The production of different particle species is recently measured in $Pb-Pb$ collisions by the ALICE experiment at $\sqrt{s}=7 $TeV. This motivates the use of various bosons and baryons measured at lower center-of-mass energies in comparing their ratios to the hadron resonance (HRG) gas model and PYTHIA event generator. It is found that the particle-to-antiparticle ratios are perfectly reproduce by means of HRG and PYTHIA at RHIC and LHC energies. The kaon-to-pion and proton-to-pion ratios are entirely overestimated by the HRG model. The PYTHIA event generator obviously underestimates the kaon…
Quark coalescence predictions for various multi-strange baryon to anti-baryon ratios for central Au+Au collisions at RHIC energies are compared to preliminary data of the STAR collaboration. The formation of Quark Matter and the sudden recombination of its constituent quarks into hadrons is found to be in agreement with these preliminary data. It seems that strange hadron and antihadron production in Au+Au collisions at RHIC is similar to that in Pb+Pb collisions at CERN SPS.
In a dynamical model of QGP at RHIC we obtain the temporal evolution of strange phase space occupancy at conditions expected to occur in 100+100A GeV nuclear collisions. We show that the sudden QGP break up model developed to describe the SPS experimental results implies dominance of both baryon and antibaryon abundances by the strange baryon and antibaryon yields.
Relativistic heavy-ion collisions lead to a final state which has a higher degree of strangeness saturation than those of elementary collisions. A systematic analysis of this phenomenon, based on the strangeness saturation factor, is made for C+C, Si+Si and Pb+Pb collisions at the CERN SPS collider and for Au+Au collisions at RHIC energies. Strangeness saturation is shown to increase with the number of participants within a colliding system, at both CERN SPS and RHIC energies. The saturation observed in central collisions of lighter nuclei deviates from that seen in peripheral collisions of he…
We analyze recent data on particle production yields obtained in p-p collisions at SPS and RHIC energies within the statistical model. We apply the model formulated in the canonical ensemble and focus on strange particle production. We introduce different methods to account for strangeness suppression effects and discuss their phenomenological verification. We show that at RHIC the midrapidity data on strange and multistrange particle multiplicity can be successfully described by the canonical statistical model with and without an extra suppression effects. On the other hand, SPS data integrat…
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.
We address the principles governing QGP hadronization and particle production in relativistic heavy-ion collisions. We argue that chemical non-equilibrium is required and show that once this condition is assumed a very good description of hadron production in collider RHIC and at LHC heavy ion experiments follows. We present results of our analysis as a function of centrality. Comparing most extreme experimental conditions we show that only the reaction volume and degree of strangeness phase space saturation change. We determine the universal QGP fireball hadronization conditions.
Chiral Lagrangians are used to compute the production rate of photons from the hadronic phase of relativistic nuclear collisions. Special attention is paid to the role of the pseudovector a_1 meson. Calculations that include reactions with strange mesons, hadronic form factors and vector spectral densities consistent with dilepton production, as well as the emission from a quark-gluon plasma and primordial nucleon-nucleon collisions, reproduce the photon spectra measured at the Super Proton Synchrotron (SPS). Predictions for the Relativistic Heavy Ion Collider (RHIC) are made.
We explore the centrality dependence of properties of the dense hadronic matter created in \sqrt{s_{NN}}=200 GeV Au--Au collisions at RHIC. Using the statistical hadronization model we fit particle yields known for 11 centrality bins. We present the resulting model parameters, rapidity yields of physical quantities and the physical properties of bulk matter at hadronization as function of centrality. We discuss the production of strangeness and entropy.
Analysis of hadron production experimental data allows to understand the properties of the dense matter fireball produced in relativistic heavy ion collisions. We interpret the analysis results and argue that color deconfined state has been formed at highest CERN-SPS energies and at BNL-RHIC.
We discuss a model for the space-time evolution of ultrarelativistic heavy-ion collisions which employs relativistic hydrodynamics within one region of the forward light-cone, and microscopic transport theory (i.e. UrQMD) in the complement. Our initial condition consists of a quark-gluon plasma which expands hydrodynamically and hadronizes. After hadronization the solution eventually changes from expansion in local equilibrium to free streaming, as determined selfconsistently by the interaction rates between the hadrons and the local expansion rate. We show that in such a scenario the inverse …
Analyses of the centrality binned identified hadron multiplicities at SPS and RHIC within the statistical-thermal model point to strangeness saturation with increasing centrality and energy.
We study the chemical freeze-out dynamics of strange particles ($K,\, Λ,\, Σ$) from a homogeneous and isotropically expanding hadronic system of $π, K, ρ, N, Λ$ and $Σ$ with zero net baryon density. We use the momentum integrated Boltzmann equation and study their evolution over the bulk hadronic matter, a condition being similar to the one created at top RHIC and LHC energies. The cross-sections, which are input to the equations, are taken either from phenomenological models or parameterized by comparing against experimental data. From this microscopic calculation we find that these strange p…
Fluctuations of conserved quantities, such as baryon, electric charge and strangeness number, are sensitive observables in relativistic heavy-ion collisions to probe the QCD phase transition and search for the QCD critical point. In this paper, we review the experimental measurements of the cumulants (up to fourth order) of event-by-event net-proton (proxy for net-baryon), net-charge and net-kaon (proxy for net-strangeness) multiplicity distributions in Au+Au collisions at $\sqrt{s_{NN}}=7.7, 11.5, 14.5, 19.6, 27, 39, 62.4, 200$ GeV from the first phase of beam energy scan program at the Relat…
The final state in The final state in heavy-ion collisions has a higher degree of strangeness saturation than the one produced in collisions between elementary particles like p-p or p-$\bar{p}$. A systematic analysis of this phenomenon is made for C-C, Si-Si and Pb-Pb collisions at the CERN SPS collider and for $Au-Au$ collisions at RHIC and at AGS energies. Strangeness saturation is shown to increase smoothly with the number of participants at AGS, CERN and RHIC energies.
Higher flow harmonics of strange hadrons in Au+Au collisions at $\sqrt{s_{NN}}$ = 200 GeV and Pb+Pb collisions at $\sqrt{s_{NN}}$ = 2.76 TeV with HYDJET++ model
We present strange particle spectra and yields measured at mid-rapidity in $\sqrt{\text{s}}=200$ GeV proton-proton ($p+p$) collisions at RHIC. We find that the previously observed universal transverse mass ($\mathrm{m_{T}}\equiv\sqrt{\mathrm{p_{T}}^{2}+\mathrm{m}^{2}}$) scaling of hadron production in $p+p$ collisions seems to break down at higher \mt and that there is a difference in the shape of the \mt spectrum between baryons and mesons. We observe mid-rapidity anti-baryon to baryon ratios near unity for $Λ$ and $Ξ$ baryons and no dependence of the ratio on transverse momentum, indicating …
