Strange Hadrons Research Articles

Study of strange quark density fluctuations in Au + Au Collisions at $$\sqrt{\textrm{s}_{_{\textrm{NN}}}}$$ = 7.7–200 GeV from AMPT Model

The strangeness production is an important observable to study the QCD phase diagram. The yield ratios of strange quark can be helpful to search for the QCD critical end point (CEP) and/or first-order phase transition. In this work, we studied the production of $$K^{\pm }$$ , $$\Xi ^-({\bar{\Xi }}^{+})$$ , $$\phi $$ and $$\Lambda ({\bar{\Lambda }})$$ in Au + Au collisions at $$\sqrt{\textrm{s}_{_{\textrm{NN}}}}$$ = 7.7, 11.5, 14.5, 19.6, 27, 39, 54.4, 62.4, and 200 GeV from A Multi-Phase Transport model with string melting version (AMPT-SM). We calculated the invariant yield of these strange hadrons using a different set of parameters compared to those reported in earlier studies and also by varying the hadronic cascade time ( $$t_{max}$$ ) in the AMPT-SM model. We also calculated the yield ratios, $${\mathcal {O}}_{K^{\pm }-\Xi ^{-}({\bar{\Xi }}^{+})-\phi -\Lambda (\bar{\Lambda })}$$ which are reported as sensitive to the strange quark density fluctuations and found that the AMPT-SM model fails to describe the non-monotonic trend observed by the experimental data. The negative particle ratio are found to be higher than the ratio of positive particles which is consistent with the experimental data. A significant effect is also seen on these ratios by varying the $$t_{max}$$ . For a crossover transition between the Quark-Gluon Plasma (QGP) and hadronic matter, the double yield ratios considered in the present study based on AMPT-SM model do not show any non-monotonic behaviors and thus providing a baseline for the search of CEP, because there is no first-order or second-order phase transition in the AMPT model. The more realistic equation of state based dynamical modeling is still required for the heavy-ion collisions in order to extract the definite physics conclusion about the non-monotonic energy dependence behavior.

Probing the incompressibility of dense hadronic matter near the QCD phase transition in relativistic heavy-ion collisions

Based on the extended hadronic transport model of relativistic heavy-ion collisions, the incompressibility of dense hadronic matter created in relativistic Au+Au heavy-ion collisions at $\sqrt{s_{NN}} = 3$ GeV is studied. By comparing experimental proton directed flow, productions of strange hadrons $\phi$, $K^{-}$ as well as their ratio $\phi/K^{-}$, proton high-order cumulants to the model calculations, a large incompressibility of dense hadronic matter is obtained from nucleon observabels while a rather small incompressibility is needed to fit the data of strange hadrons. This may indicate hadronic matter possesses different incompressibilities in different density regions, i.e., the incompressibility may become stiffer from saturation density to a certain baryon density and then turn to soft before reaching hadron-quark phase transition. The study also shows that the incompressibility significantly affects the critical baryon density of hadron-quark phase transition.

Systematic analysis of the pp collisions at LHC energies with Tsallis function

This work focuses on the study of identified (, , p, and ), strange hadrons (, Λ, ), recorded by CMS, and light nuclei and their anti-nuclei (d, , t, , 3He and ), recorded by ALICE, at , 2.76 TeV, 7 TeV and 13 TeV in pp collision at mid rapidities. The p T distributions of these particles are analyzed using the Tsallis model, which fits the experimental data very well. Several important parameters for studying the characteristics of the medium produced during such collisions are extracted. The effective temperature (T) increases monotonically with increasing particle mass and also with increasing collision energy. The non-extensivity parameter (q) decreases with the mass of the particle. For heavier particles, greater T and smaller q mean that they decouple early from the system and attain equilibrium quickly compared to lighter ones. Furthermore, with an increase in collision energy, the multiplicity parameter N 0 increases.

Collision centrality and energy dependence of strange hadron production in Au + Au collisions at sNN=7.7 –54.4 GeV

We apply an equal-velocity quark combination model to systematically study the transverse momentum (${p}_{T}$) spectra of identified hadrons ${K}_{S}^{0}, \ensuremath{\phi}, \mathrm{\ensuremath{\Lambda}}, {\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}, {\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}, \overline{\mathrm{\ensuremath{\Lambda}}}, {\overline{\mathrm{\ensuremath{\Xi}}}}^{+}, {\overline{\mathrm{\ensuremath{\Omega}}}}^{+}, p, \overline{p}, {\ensuremath{\pi}}^{+}$, and ${\ensuremath{\pi}}^{\ensuremath{-}}$ at midrapidity in $\mathrm{Au}+\mathrm{Au}$ collisions at $\sqrt{{s}_{NN}}=7.7$, 11.5, 19.6, 27, 39, 54.4 GeV. The relative deviation between model calculations and experimental data of these 12 hadrons is generally about 10% in central collisions even at low collision energies and is weakly increased in peripheral collisions. We systematically explain the dependence of two baryon-to-meson ratios $\overline{\mathrm{\ensuremath{\Lambda}}}/{K}_{S}^{0}$ and $\mathrm{\ensuremath{\Omega}}/\ensuremath{\phi}$ on ${p}_{T}$, collision centrality, and collision energy by the property of quark ${p}_{T}$ spectra at hadronization. We derive the analytic relations between ${R}_{CP}$ of hadrons and those of quarks, and we use them to naturally explain the species and ${p}_{T}$ dependence of ${R}_{CP}$ of those strange hadrons.

Production and enhancement of (multi-) strange hadrons in Au+Au collisions at sNN=200 GeV RHIC energy and Pb+Pb collisions at sNN=2.76 TeV LHC energy

In this article, we investigate $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Pb}+\mathrm{Pb}$ collision systems to understand the (multi-) strange hadron production at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies using the Monte Carlo $\mathrm{HYDJET}++$ model. We study the ${p}_{T}$ spectra, particle ratios, and strangeness enhancement factor for (multi-) strange hadrons. The ${p}_{T}$ spectra of ${K}^{+}({K}^{\ensuremath{-}})$, ${K}_{s}^{0}$, $\mathrm{\ensuremath{\Lambda}}(\overline{\mathrm{\ensuremath{\Lambda}}})$, ${\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}({\overline{\mathrm{\ensuremath{\Xi}}}}^{+})$, and ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}({\overline{\mathrm{\ensuremath{\Omega}}}}^{+})$ are shown for both $\mathrm{Au}+\mathrm{Au}$ and $\mathrm{Pb}+\mathrm{Pb}$ collision systems in various centrality intervals. We find that the strange quark thermalization might not be achieved by the model for multistrange baryons toward peripheral collisions. The ${p}_{T}$-differential particle ratios, focused on strange hadron-to-meson ratios, are reported for 0--5% and 40--60% centrality intervals for both the collision systems. We observe an enhancement in the particle ratios at intermediate ${p}_{T}$ region. ${p}_{T}$ integrated strange-to-nonstrange ratios suggest that chemical equilibrium might not be achieved for multistrange hadrons. We report the strangeness enhancement factor for $\mathrm{\ensuremath{\Lambda}}(\overline{\mathrm{\ensuremath{\Lambda}}})$, ${\mathrm{\ensuremath{\Xi}}}^{\ensuremath{-}}({\overline{\mathrm{\ensuremath{\Xi}}}}^{+})$, and ${\mathrm{\ensuremath{\Omega}}}^{\ensuremath{-}}+{\overline{\mathrm{\ensuremath{\Omega}}}}^{+}$ at both RHIC and LHC energies. An increase in the enhancement factor is observed with the increase in strangeness content of the baryons. We also observe that enhancement is higher in $\mathrm{Au}+\mathrm{Au}$ collisions than in $\mathrm{Pb}+\mathrm{Pb}$ collisions. Further, we compare the $\mathrm{HYDJET}++$ results with the experimental data and various other simulation models, wherever possible.

Production of Strange and Charm Hadrons in Pb+Pb Collisions at sNN = 5.02 TeV

Using a quark combination model with the equal-velocity combination approximation, we study the production of hadrons with strangeness and charm flavor quantum numbers in Pb+Pb collisions at sNN= 5.02 TeV. We present analytical expressions and numerical results for these hadrons’ transverse momentum spectra and yield ratios. Our numerical results agree well with the experimental data available. The features of strange and charm hadron production in the quark–gluon plasma at the early stage of heavy ion collisions are also discussed.

Elliptic flow of strange and multi-strange hadrons in isobar collisions at √SNN = 200 GeV at RHIC

We report the elliptic flow (υ2) of Ks0, Λ, Ξ¯+, ϕ, Ξ−, and Ξ+ at midrapidity for Ru+Ru and Zr+Zr collisions at √SNN = 200 GeV. The transverse momentum (pT) and centrality dependence of υ2 have been studied. The number of constituent quark (NCQ) scaling for all the (multi-)strange hadrons has also been tested. The dependence in the ratio of average υ2 (〈υ2〉) on centrality shows a deviation from unity indicating a difference in nuclear structure and deformation between the isobars. The results show a systematic size dependence when compared to Cu+Cu, Au+Au, and U+U collisions at similar beam energies.

Elliptic and triangular flow of (multi-)strange hadrons and ɸ mesons in BES-II energies at STAR

In these proceedings, we present the measurements of elliptic (v2) and triangular (v3) flow of (multi-)strange hadrons and ϕ mesons in 19.6 and 14.6 GeV Au+Au collisions from the STAR. The number of constituent quark (NCQ) scaling of v2 and v3 holds well at √SNN=19.6 GeV, which indicates the collective flow is built up in the partonic stage. At these energies, the anti-particles show better NCQ scaling than the particles for both v2 and v3, which may be caused by the different contributions from the produced and transported quarks.

Strange Hadron Production in Au+Au Collisions at RHIC Beam Energy Scan

Strangeness production has been suggested to be a sensitive probe to the early-time dynamics of the nuclear matter created in heavy-ion collisions. Transverse momentum distributions and yields of strange hadrons provide important information on their production mechanisms and can help us probe the properties of the created medium and its evolution. Thanks to the high statistics data taken during the STAR BES-II program in 2018-2021, a series of measurements on the properties of strangeness production at low energies are carried out. In these proceedings, the production of K−, KS0, ϕ, Λ, and Ξ− in Au+Au collisions at √SNN = 3 GeV are presented. The strange hadron transverse momentum spectra, rapidity density distributions, and particle ratios are shown. These results are compared with UrQMD model calculations, and the extracted kinetic freeze-out parameters are discussed and compared with the ones from higher collision energies.

Femtoscopy of Proton, Light Nuclei, and Strange Hadrons in Au\(+\)Au Collisions at STAR

In these proceedings, we present the measurements of proton, light nuclei, and strange particle with neutral kaons correlation functions in Au+Au collisions at the BES program and top RHIC energy. The experimental results will be compared with model calculations to extract the size of emitting source and the properties of final state interactions. The collision energy and centrality dependence of the source size will be studied. Further, the implications for the production mechanism of light nuclei will be discussed.

Study of strange particle pT spectra in heavy-ion collisions at relativistic energies

The transverse momentum distributions of strange and multi-strange hadrons produced in most central Au+Au collisions at RHIC-BES energies were studied using the Boltzmann-Gibbs blast-wave model. The energy dependence of the kinetic freeze-out parameters is presented and discussed.

Production Yield and Azimuthal Anisotropy Measurements of Strange Hadrons from BES at STAR

Production Yield and Azimuthal Anisotropy Measurements of Strange Hadrons from BES at STAR

Exploration of the phase diagram within a transport approach

We study equilibrium as well as out-of-equilibrium properties of the strongly interacting QGP medium under extreme conditions of high temperature T and high baryon densities or baryon chemical potentials μB within a kinetic approach. We present the thermodynamic and transport properties of the QGP close to equilibrium in the framework of effective models with Nf=3 active quark flavours such as the Polyakov extended Nambu-Jona Lasinio (PNJL) and dynamical quasiparticle model with the CEP (DQPM-CP). Considering the transport coefficients and the EoS of the QGP phase, we compare our results with various results from the literature. Furthermore, out-of equilibrium properties of the QGP medium and in particular, the effect of a μB- dependence of thermodynamic and transport properties of the QGP are studied within the Parton-Hadron-String-Dynamics (PHSD) transport approach, which covers the full evolution of the system during HICs. We find that bulk observables and flow coefficients for strange hadrons as well as for antiprotons are more sensitive to the properties of the QGP, in particular to the μB - dependence of the QGP interactions.

Study of Bulk Properties of Strange Particles in Au+Au Collisions at sNN = 54.4 GeV.

We analyzed the transverse momentum pT spectra of various strange hadrons KS0, Λ(Λ¯) and Ξ-(Ξ¯+) at mid-rapidity (y) in different centrality intervals from Au+Au collisions at sNN= 54.4 GeV. The pT spectra of these strange hadrons are investigated by the Tsallis-like distribution, which satisfactorily fits the experimental data. The bulk properties of the medium produced in ultra-relativistic heavy-ion collisions at the kinetic freeze-out are reflected by measuring the hadron spectra. The effective temperature T, transverse flow velocity βT, and mean pT along with other parameters that are strongly dependent on centrality and particle specie are extracted. The effective temperature of multi-strange particle (Ξ-(Ξ¯+)) is larger as compared to singly-strange particles Λ(Λ¯) and KS0. Furthermore, the kinetic freeze-out temperature T, transverse flow velocity βT. and mean pT (⟨pT⟩) show a decreasing trend towards lower centrality, while the entropy parameter q increases from central to peripheral collisions. In addition, a positive correlation of ⟨pT⟩ and T and a negative correlation of q and T are also reported.

Strangeness enhancement across collision systems without a plasma

We present novel rope hadronization results for strange hadron enhancement in pp, pPb, and PbPb collisions using PYTHIA/Angantyr at LHC energies. With the rope model for string fragmentation, we find that the strangeness and baryon enhancement has a coherent increase across all collision systems as a function of average charged central multiplicity, in qualitative agreement with LHC data. In AA collisions, we find that the baryonic yields overshoot data at high multiplicities, and we discuss how a combination of rope hadronization with other string interactions may tame this rise.

Strangeness Production from Proton–Proton Collisions at Different Energies by Using Monte Carlo Simulation

Nuclear matter, at sufficiently energy density and high temperature, undergoes a transition to a state of strongly interacting QCD matter in which quarks and gluons are not confined known as the Quark–Gluon Plasma (QGP). QGP is usually produced in high-energy collisions of heavy nuclei in the laboratory, where an enhancement of strange hadrons’ production is observed. Many of the effects which are typical of heavy ion phenomenology have been observed in high-multiplicity proton–proton (pp) collisions. The enhancement of strange particles’ production in pp collisions was reported at s=7 TeV and s=13 TeV in 2017 and 2020, respectively, and it was found that the integrated yields of strange particles, relative to pions, increase notably with the charged-particle multiplicity of events. Here, we report the multiplicity dependence of strange particles at |y|<0.5 in pp collisions at s = 7 TeV, 13 TeV, 20 TeV, and 27 TeV from a Monte Carlo simulation using PYTHIA8, EPOS-LHC, and Herwig7.

Analyses of the collective properties of hadronic matter in Au-Au collisions at 54.4 GeV

We investigated the strange hadrons transverse momentum (${p}_{T}$) spectra in Au-Au collision at $\sqrt{{s}_{NN}}=54.4\text{ }\text{ }\mathrm{GeV}$ in the framework of modified Hagedorn function with embedded flow. It is found that the model can describe the particle spectra well. We extracted the kinetic freeze-out temperature ${T}_{0}$, transverse flow velocity ${\ensuremath{\beta}}_{T}$, kinetic freeze-out volume $V$, mean transverse momentum $⟨{p}_{T}⟩$, the entropy parameter $n$, and the multiplicity parameter ${N}_{0}$. We reported that all these parameters increase towards the central collisions. The larger kinetic freeze-out temperature, transverse flow velocity, kinetic freeze-out volume, and the entropy parameter ($n$) in central collisions compared to peripheral collisions show the early decoupling of the particles in central collisions. In addition, all the above parameters are mass dependent. The kinetic freeze-out temperature (${T}_{0}$), the entropy parameter $n$, and mean transverse momentum ($⟨{p}_{T}⟩$) are larger for massive particles, while the transverse flow velocity (${\ensuremath{\beta}}_{T}$), kinetic freeze-out volume ($V$), and the multiplicity parameter (${N}_{0}$) show the opposite behavior. Larger ${T}_{0}$, $n$, and smaller ${\ensuremath{\beta}}_{T}$ as well as $V$ of the heavier particles indicate the early freeze-out of the heavier particles, while larger $⟨{p}_{T}⟩$ for the heavier particles evince that the effect of radial flow is stronger in heavier particles. The separate set of parameters for each particle shows the multiple kinetic freeze-out scenario, where the mass-dependent kinetic freeze-out volume shows the volume differential freeze-out scenario. We also checked the correlation among different parameters, which include the correlation of ${T}_{0}$ and ${\ensuremath{\beta}}_{T}$, ${T}_{0}$ and $V$, ${\ensuremath{\beta}}_{T}$ and $V$, $⟨{p}_{T}⟩$ and ${T}_{0}$, $⟨{p}_{T}⟩$ and ${\ensuremath{\beta}}_{T}$, $⟨{p}_{T}⟩$, and $V$, $n$ and ${T}_{0}$, $n$ and ${\ensuremath{\beta}}_{T}$, and $n$ and $V$, and they all are observed to have positive correlations with each other which validates our results.

Study of strange particle pT spectra in relativistic heavy-ion collisions with blast-wave model

Boltzmann–Gibbs blast-wave model was used to analyze the transverse momentum distributions of strange hadrons ([Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text]) produced in most central Au+Au collisions at RHIC-BES energies. The kinetic freeze-out parameters for energies [Formula: see text][Formula: see text] are presented and discussed as a function of collision energy. The [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], [Formula: see text], and [Formula: see text] BGBW fit results are similar within errors with the kinetic freeze-out parameters of bulk hadrons ([Formula: see text], [Formula: see text], p and [Formula: see text]). The multi-strange kinetic freeze-out parameters indicate that these hadrons tend to decouple earlier from the system than the bulk hadrons, having a smaller average transverse flow velocity.

Multi-differential studies to explore strangeness enhancement in pp with ALICE at the LHC

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, which is estimated by an anti-correlation with the energy deposited in ALICE's Zero Degree Calorimeters. The results indicate that strangeness production emerges from the growth of the underlying event and confirm it is related to the final state multiplicity.

Studying the mechanisms for strange particle production with ALICE at LHC

The main goal of the ALICE experiment is to study the physics of strongly interacting matter, focusing on the properties of the quark-gluon plasma (QGP). The relative production of strange hadrons with respect to non-strange hadrons in heavy-ion collisions was historically considered as one of the signatures of QGP formation. However, the latest results in proton-proton (pp) and proton-lead (p-Pb) collisions have revealed an increasing trend in the yield ratio of strange hadrons to pions with the charged-particle multiplicity in the event, showing a smooth evolution across different collision systems and energies. We present the new studies which are performed with the aim of better understanding the production mechanisms for strange particles and hence the strangeness enhancement phenomenon in small collision systems. In one of the recent studies, the very forward energy transported by beam remnants (spectators) and detected by the Zero Degree Calorimeters (ZDC) is used to classify events. The contribution of the effective energy and the particle multiplicity on strangeness production is studied using a multi-differential approach in order to disentangle initial and final state effects. In the second study, the origin of strangeness enhancement with multiplicity in pp has been further investigated by separating the contribution of soft and hard processes, such as jets, to strange hadron production. Techniques involving full jet reconstruction or two-particle correlations have been exploited. The results indicate that the increased relative strangeness production emerges from the growth of the underlying event, being disconnected from initial state properties, and suggest that soft (out-of-jets) processes are the dominant contribution to strange hadron production.