Production Of Strange Hadrons Research Articles

A test of strangeness quantum number conservation in proton-proton collisions

The study delves into the production of (multi-) strange hadrons in proton-proton collisions at LHC. Novel observables are proposed to distinguish between Epos4, based on core-corona separation between a thermalised QGP phase and a vacuum phase with global strangeness conservation, and Pythia 8.3, based on microscopic interactions between Lund strings that conserve strangeness locally. Correlations between a ϕ\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\phi $$\\end{document} meson and (multi-)strange hadrons are shown to be an excellent discriminator between the two types of models.

P T -spectra, nuclear modification factors (R AA , and R CP ) of (multi-) strange hadrons in Au+Au collisions at sNN= 200 GeV with HYDJET++

In this article, we have reported the transverse momentum (p T ) spectra and nuclear modification factors of (multi-) strange hadrons produced in Au+Au collisions at sNN= 200 GeV using the Monte Carlo HYDJET++ model. For the present study, we have tuned few of the input parameters, in both soft as well as hard parts, of the model to appropriately describe the production of (multi-) strange hadrons. We have presented the p T -spectra of (multi-) strange hadrons in different centrality intervals. On comparing p T -spectra with the experimental data, we observe that the model does not achieve thermal equilibrium for kaons toward peripheral collisions and for omega baryons for all the centrality intervals. The R AA results obtained by the model reproduce the experimental data well while the R CP results show less suppression at higher p T than the experimental data. Further, HYDJET++ results are also compared with different theoretical models and discussed, wherever possible.

Monte Carlo predictions for the production of primary and strange Hadrons at LHC energies and study of the thermal properties of system

Monte Carlo predictions for the production of primary and strange Hadrons at LHC energies and study of the thermal properties of system

Probing the interplay of multiplicity and effective energy on strangeness production in pp collisions with ALICE

The strong interaction between quarks and gluons, the elementary constituents of the hadronic matter, is described by quantum chromodynamics (QCD). Under extreme conditions of high temperature and energy density, the QCD predicts a transition from the hadronic phase to a colour deconfined medium called quark-gluon plasma (QGP). The QGP can be investigated in the laboratory through ultrarelativistic heavy-ion collisions, such as the ones between lead (Pb) ions at the Large Hadron Collider (LHC) at CERN. The enhanced production of strange hadrons in heavy-ion collisions with respect to proton-proton (pp) collisions was historically considered one of the signatures of QGP formation. At the LHC, the ALICE Collaboration observed that the ratio of strange to non-strange hadron yields increases with the charged-particle multiplicity at midrapidity, starting from pp collisions and evolving smoothly across larger interaction systems and energies, ultimately reaching Pb-Pb collisions. The origin of this effect in small collision systems remains an open question. This work exploits a novel approach to study strangeness production in pp collisions, introducing, for the first time, the concept of effective energy in hadronic collisions at the LHC.

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.

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.

Production of strange hadrons in jets and underlying events in pp and p–Pb collisions with ALICE

The production of strange (, Λ) and multi-strange (Ξ± and Ω±) hadrons in jets and underlying events in pp and p–Pb collisions is studied with ALICE at the LHC. Transverse momentum (p T) differential density distribution of particles produced in a jet is compared to that of inclusive particle production and that in underlying events. The particle yield ratios of and as a function of p T are also investigated in jets and underlying events. The production of the multi-strange hadrons, Ξ± and Ω±, and the corresponding ratio in jets and underlying events are measured for the first time. The p T-differential density distribution of hadrons associated with hard scattering decreases slower than that for inclusive production. The baryon-to-meson and baryon-to-baryon ratios measured in jets exhibit clear differences from values obtained from the inclusive spectra in the intermediate p T range. The p T distribution of strange hadrons produced in jets is also studied in pp collisions at and and in p–Pb collisions at . The p T spectra of particle produced in jets are independent of collision systems and collision energies. No apparent collision energy and collision system dependence is observed for the particle yield ratios of and associated with energetic jets. These new results are compared to PYTHIA 8 event generator. The ratio are generally reproduced by the model, but large discrepancies between data and PYTHIA simulations are observed for .

Strange Hadron Production in Au+Au Collisions at √SNN = 54.4 GeV

The RHIC Beam Energy Scan (BES) program was proposed to study the QCD phase transition. As a sensitive probe to the transition from the hadron gas to the Quark-Gluon Plasma, the particle ratios of strange hadrons are measured to study the properties of nuclear matter. Recently, the production of strange hadrons (KS0, Λ, Ξ, Ω, and ϕ) at mid-rapidity (|y|<0.5) in Au+Au collisions at √SNN = 54.4 GeV were measured by the STAR experiment at RHIC. In this paper nuclear modification factor, baryon-to-meson ratio, as well as the overall integrated yields of these strange hadrons at √SNN = 54.4 GeV are presented. In particular, the multi-strange baryon-to-meson ratio N(Ω− + Ω¯+)/[2N(ϕ)] is studied and compared to previous measurements from other BES energies. The strange-hadron-to-pion ratios versus charged hadron multiplicity are also studied and compared to the measurements in heavy-ion collisions at higher energies.

Investigating the origin of strangeness enhancement in small systems through multi-differential analyses

The main goal of the ALICE experiment is to study the physics of strongly interacting matter, including 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, measurements at the LHC in pp and p-Pb collisions have shown similar features to those observed in Pb-Pb, measuring an increase in the production of strange hadrons relative to pions with the charged-particle multiplicity in the event. In order to better understand the role of the event multiplicity to the observed enhancement in pp, two new complementary analyses have been performed. The first exploits the angular correlation between strange and high-pT hadrons in the event to classify in-jet and out-of-jet strangeness production. The second uses the concept of the effective energy available in the event for particle production which is estimated by an anti-correlation with the energy deposited in ALICE’s Zero Degree Calorimeters. The results suggest that strangeness enhancement emerges from the growth of the underlying event and is not connected to initial state properties.

Multiplicity dependence of freezeout scenarios in pp collisions at s=7 TeV

The data on transverse momentum integrated hadron yields in different multiplicity classes of $p+p$ collisions at $\sqrt{s}=7$ TeV have been analyzed to extract the chemical freeze-out parameters using a thermal model. The chemical freeze-out parameters have been extracted for three different freeze-out schemes: (i) unified freeze-out for all hadrons in complete thermal equilibrium (1CFO), (ii) unified freeze-out for all hadrons with an additional parameter ${\ensuremath{\gamma}}_{S}$ which accounts for possible out-of-equilibrium production of strange hadrons ($1\mathrm{CFO}+{\ensuremath{\gamma}}_{S}$), and (iii) separate freeze-out for hadrons with and without strangeness content (2CFO). It has been observed that the $1\mathrm{CFO}+{\ensuremath{\gamma}}_{S}$ scheme gives the best description of the hadronic yields at midrapidity when multiplicity ($\ensuremath{\langle}d{N}_{ch}/d\ensuremath{\eta}\ensuremath{\rangle}$) of the collision is less than 10. This indicates that the strangeness is out of equilibrium in most of the multiplicity classes of $p+p$ collisions. All three parameters of this CFO scheme, temperature $T$, radius $R$ of the fireball, and strangeness suppression factor ${\ensuremath{\gamma}}_{S}$ increase with the increase of $\ensuremath{\langle}d{N}_{ch}/d\ensuremath{\eta}\ensuremath{\rangle}$. Furthermore, we have compared applicability of different CFO schemes considering two more colliding systems $p+\text{Pb}$ at $\sqrt{{s}_{\mathrm{NN}}}=5.02$ and $\text{Pb}+\text{Pb}$ at $\sqrt{{s}_{\mathrm{NN}}}=2.76$ TeV along with $p+p$ collisions at $\sqrt{s}=7$ TeV. We observe a freeze-out volume (or multiplicity) dependence of CFO schemes regardless of colliding ions. The $1\text{CFO}+{\ensuremath{\gamma}}_{S}$, 1CFO, and 2CFO schemes provide the best description of the data when the dimensionless quantity $V{T}^{3}$ approximately satisfies the conditions $V{T}^{3}<50, 50<V{T}^{3}<100$, and $V{T}^{3}>100$, respectively, or the corresponding multiplicity satisfies the conditions $\ensuremath{\langle}d{N}_{ch}/d\ensuremath{\eta}\ensuremath{\rangle}<30, 30<d{N}_{ch}/d\ensuremath{\eta}<60$, and $\ensuremath{\langle}d{N}_{ch}/d\ensuremath{\eta}\ensuremath{\rangle}>100$, respectively.

Evolution of strange and multi-strange hadron production with relative transverse multiplicity activity in underlying event

In this work, the relative Underlying event (UE) transverse multiplicity activity classifier (R_mathrm{{T}}) is used to study the strange and multi-strange hadron production in proton-proton collisions. Our study with R_mathrm{{T}} would allow to disentangle these particles, which are originating from the soft and hard QCD processes. We have used the PYTHIA 8 Monte-Carlo (MC) with a different implementation of color reconnection and rope hadronization models to demonstrate the proton-proton collisions data at sqrt{s}~= 13 TeV. The relative production of strange and multi-strange hadrons are discussed extensively in low and high transverse activity regions. In this contribution, the relative strange hadron production is enhanced with increasing R_mathrm{{T}}. This enhancement is significant for the strange baryons as compared to mesons. In addition, the particle ratios as a function of R_mathrm{{T}}~confirm the baryon enhancement in new Color Reconnection (newCR), whereas the Rope model confirms the baryon enhancement only with strange quark content. Experimental confirmation of such results will provide more insight into the soft physics in the transverse region, which will be useful to investigate various tunes based on hadronization and color reconnection schemes.

Microscopic study of strange hadron production at the LHC with sNN=2.76 TeV

Ratio of the yield of strange hadrons to pions is considered as an important observable in studying the properties of the system produced in relativistic heavy ion collisions. Production of strange hadrons $K, \bar{K}, \Lambda, \Sigma, \Xi$ and $\Omega$ have been evaluated microscopically using rate equations by considering their hadronic interaction cross sections in an expanding medium. The yields obtained from rate equations are normalized with thermal pions and compared with the measurements from Pb-Pb collisions at various multiplicities at LHC energy. The calculation has been done for various initial and freeze out conditions. At 2760 GeV, LHC energy, $\Lambda, \Xi, \Omega$ freeze out close to $T_C$ and $K^0_s$ freezes out little later. But there is a subtle difference in freeze out temperatures of different species which may be distinguishable at lower colliding energies.

Strangeness production with ALICE at the LHC

The main goal of the ALICE experiment is to study the physics of strongly interacting matter under extremely high temperature and energy density conditions to investigate the properties of the Quark-Gluon plasma (QGP). The enhanced production of strange hadrons with respect to non-strange particles was historically considered as one of the signatures of QGP formation during the evolution of the system created in heavy-ion collisions. The excellent tracking and particle identification capabilities of the ALICE experiment allow the reconstruction of multi-strange baryons via their weak decay channels over a large range of transverse momentum. The yields and the relative production rates of strange and multi-strange particles normalized to pions measured in pp, p–Pb, Pb–Pb and Xe–Xe collisions are presented as a function of particle multiplicity. The strangeness production dependence on the collision energy is also shown. Results are compared to QCD-inspired and statistical hadronization model predictions.

Effect of rope hadronization on strangeness enhancement in p−p collisions at LHC energies

The p$-$p collisions at high multiplicity at LHC show small scale collective effects similar to that observed in heavy ion collisions such as enhanced production of strange and multi-strange hadrons, long range azimuthal correlations, etc. The observation of strangeness enhancement in p$-$p collisions at at $\sqrt{s}$ = 7 TeV and 13 TeV as measured by ALICE experiment is explored using Pythia8 event generator within the framework of microscopic rope hadronization model which assumes the formation of ropes due to overlapping of strings in high multiplicity environment. The transverse momentum ($p_{T}$) spectra shape and its hardening with multiplicity is well described by the model. The mechanism of formation of ropes also described the observed experimental strangeness enhancement for higher multiplicity classes in p$-$p collisions at 7 TeV and 13 TeV. The enhancement with multiplicity is further investigated by studying the mean $p_{T}$ ($<p_{T}>$) and the integrated yields ($<dN/dy>$ ) of strange and multi-strange hadrons and comparing the predictions to the measured data at LHC for 7 TeV and 13 TeV.

Strangeness production via resonances in heavy-ion collisions at energies available at the GSI Schwerionensynchrotron

Production of strange hadrons in elementary and heavy-ion reactions is studied with the hadronic transport approach SMASH (Simulating Many Accelerated Strongly-interacting Hadrons). The poorly known branching ratios of the relevant hadronic resonances are constrained from the known elementary hadronic cross sections and from invariant mass spectra of dileptons. The constrained model is employed as a baseline to compare to heavy-ion-collision experiments at low energies ($E_\text{kin} = 1-2A\,\text{GeV}$) and to predict some of the upcoming pion-beam results by HADES, which are expected to be sensitive to the resonance properties. The employed vacuum-resonance approach proves to be viable for small systems at these energies, but for large systems additional in-medium effects might be required.

Studying Strangeness Production with HADES

The High-Acceptance DiElectron Spectrometer (HADES) operates in the 1 - 2A GeV energy regime in fixed target experiments to explore baryon-rich strongly interacting matter in heavy-ion collisions at moderate temperatures with rare and penetrating probes. We present results on the production of strange hadrons below their respective NN threshold energy in Au+Au collisions at 1.23A GeV ([see formula in PDF] = 2.4 GeV). Special emphasis is put on the enhanced feed-down contribution of ϕ mesons to the inclusive yield of K- and its implication on the measured spectral shape of K-. Furthermore, we investigate global properties of the system, confronting the measured hadron yields and transverse mass spectra with a Statistical Hadronization Model (SHM) and a blastwave parameterization, respectively. These supplement the world data of the chemical and kinetic freeze-out temperatures.

Strangeness production in Pb-Pb collisions at LHC energies with ALICE

The results on the production of strange and multi-strange hadrons (K0S, Λ, Ξ and Ω) measured with ALICE in Pb-Pb collisions at the top LHC energy of [see formula in PDF] = 5.02 TeV are reported. Thanks to its excellent tracking and particle identification capabilities, ALICE is able to measure weakly decaying particles through the topological reconstruction of the identified hadronic decay products. Results are presented as a function of centrality and include transverse momentum spectra measured at central rapidity, pT-dependent Λ/K0S ratios and integrated yields. A systematic study of strangeness production is of fundamental importance for determining the thermal properties of the system created in ultrarelativistic heavy ion collisions. In order to study strangeness enhancement, the yields of studied particles are normalised to the corresponding measurement of pion production in the various centrality classes. The results are compared to measurements performed at lower energies, as well as to different systems and to predictions from statistical hadronization models.

Chiral symmetry restoration versus deconfinement in heavy-ion collisions at high baryon density

We study the production of strange hadrons in nucleus-nucleus collisions from 4 to 160 A GeV within the Parton-Hadron-String Dynamics (PHSD) transport approach that is extended to incorporate essentials aspects of chiral symmetry restoration (CSR) in the hadronic sector (via the Schwinger mechanism) on top of the deconfinement phase transition as implemented in PHSD. Especially the $K^+/\pi^+$ and the $(\Lambda+\Sigma^0)/\pi^-$ ratios in central Au+Au collisions are found to provide information on the relative importance of both transitions. The modelling of chiral symmetry restoration is driven by the pion-nucleon $\Sigma$-term in the computation of the quark scalar condensate $<q {\bar q}>$ that serves as an order parameter for CSR and also scales approximately with the effective quark masses $m_s$ and $m_q$. Furthermore, the nucleon scalar density $\rho_s$, which also enters the computation of $<q {\bar q}>$, is evaluated within the nonlinear $\sigma-\omega$ model which is constraint by Dirac-Brueckner calculations and low energy heavy-ion reactions. The Schwinger mechanism (for string decay) fixes the ratio of strange to light quark production in the hadronic medium. We find that above $\sim$80 A GeV the reaction dynamics of heavy nuclei is dominantly driven by partonic degrees-of-freedom such that traces of the chiral symmetry restoration are hard to identify. Our studies support the conjecture of 'quarkyonic matter' in heavy-ion collisions from about 5 to 40 A GeV and provide a microscopic explanation for the maximum in the $K^+/\pi^+$ ratio at about 30 A GeV which only shows up if a transition to partonic degrees-of-freedom is incorporated in the reaction dynamics and is discarded in the traditional hadron-string models.

STAR results on strangeness production in beam energy scan program

We present the recent STAR results on the production of strange hadrons (K0s, ϕ, Λ, Ξ and Ω) in √sNN= 7.7 — 39 GeV Au+Au collisions in the RHIC beam energy scan program. We investigate the strangeness enhancement and strangeness equilibration as a function of beam energy and system size at RHIC. Nuclear modification factors and particle ratios will be highlighted. Implications on partonic vs. hadronic dynamics as a function of the beam energy will be discussed.

(Anti-)strangeness production in heavy-ion collisions

The production and dynamics of strange and antistrange hadrons in heavy-ion reactions from √sNN ≈ 3 GeV to 200 GeV is analyzed within the Parton-Hadron-String- Dynamics (PHSD) transport model. The PHSD results for strange baryon and antibaryon production are roughly consistent with the experimental data starting from upper SPS energies. Nevertheless, hadronic final state flavor-exchange reactions are important for the actual abundances, in particular at large rapidities where hadronic dynamics, parton fragmentation and string decay dominate. A striking disagreement between the PHSD results and the available data persists, however, for bombarding energies below √sNN ≈ 8 GeV where the strangeness production is significantly underestimated as in earlier HSD studies. This finding implies that the strangeness enhancement seen experimentally at FAIR/NICA energies cannot be attributed to a deconfinement phase transition or crossover but probably involves the approximate restoration of chiral symmetry in the hadronic phase.References