Strange Hadrons Research Articles

Hybrid model approach for strange and multistrange hadrons in2.76ATeVPb+Pbcollisions

Using the VISHNU hybrid model, we calculate the multiplicity, spectra, and elliptic flow of $\ensuremath{\Lambda},\phantom{\rule{0.16em}{0ex}}\ensuremath{\Xi}$, and $\ensuremath{\Omega}$ in $2.76A$ TeV Pb + Pb collisions. Comparisons between our calculations and the ALICE measurements show that the model generally describes the soft hadron data of these strange and multistrange hadrons at several centrality bins. Mass ordering of elliptic flow among $\ensuremath{\pi},\phantom{\rule{0.16em}{0ex}}K,\phantom{\rule{0.16em}{0ex}}p,\phantom{\rule{0.16em}{0ex}}\ensuremath{\Lambda},\phantom{\rule{0.16em}{0ex}}\ensuremath{\Xi}$, and $\ensuremath{\Omega}$ has also been studied and discussed. With a nice description of the particle yields, we explore chemical and thermal freeze-out of various hadrons species at the Large Hadron Collider within the framework of the VISHNU hybrid model.

V0 Reconstruction of Strange Hadrons in Au+Au Collisions at 1.23 AGeV with HADES

Preliminary results on the production of weakly decaying strange hadrons are reported for collisions of Au+Au at 1.23 AGeV beam energy studied with the HADES detector at GSI in Darmstadt. At this collision energy all strange particles are created below their elementary threshold. The reconstruction of the investigated particles (i.e. Λ and K0s) via the topology of their charged decay products (V0 reconstruction) is presented in detail. From the corrected yields of Λ and K0s the ratio K0S/Λ can be calculated and included into a statistical model fit.

Long-range two-particle correlations of strange hadrons with charged particles in pPb and PbPb collisions at LHC energies

Measurements of two-particle angular correlations between an identified strange hadron (KS0 or Λ/Λ‾) and a charged particle, emitted in pPb collisions, are presented over a wide range in pseudorapidity and full azimuth. The data, corresponding to an integrated luminosity of approximately 35 nb−1, were collected at a nucleon–nucleon center-of-mass energy (sNN) of 5.02 TeV with the CMS detector at the LHC. The results are compared to semi-peripheral PbPb collision data at sNN=2.76 TeV, covering similar charged-particle multiplicities in the events. The observed azimuthal correlations at large relative pseudorapidity are used to extract the second-order (v2) and third-order (v3) anisotropy harmonics of KS0 and Λ/Λ‾ particles. These quantities are studied as a function of the charged-particle multiplicity in the event and the transverse momentum of the particles. For high-multiplicity pPb events, a clear particle species dependence of v2 and v3 is observed. For pT<2 GeV, the v2 and v3 values of KS0 particles are larger than those of Λ/Λ‾ particles at the same pT. This splitting effect between two particle species is found to be stronger in pPb than in PbPb collisions in the same multiplicity range. When divided by the number of constituent quarks and compared at the same transverse kinetic energy per quark, both v2 and v3 for KS0 particles are observed to be consistent with those for Λ/Λ‾ particles at the 10% level in pPb collisions. This consistency extends over a wide range of particle transverse kinetic energy and event multiplicities.

Angular Momentum and Polarization in Hadron Collisions up to LHC Energies

Longstanding puzzles in spin physics can be confronted at the high energies of the LHC. Heavy quarks will be produced with significant polarization, both as single spin asymmetries and through polarization correlations. Lower energy proton accelerator and leptoproduction data suggest various mechanisms within QCD for polarization phenomena that can be tested at higher energies. Observation of strange and charm hadron polarization reveals important aspects of QCD spin physics. Top quark polarization is predicted to be significant, and polarization correlations will reveal important aspects of the gluon distributions of the hadrons.

SU(3) group structure of strange flavor hadrons

We provide the isoscalar factors of the SU(3) Clebsch-Gordan series 8⊗35 which are extensions of the previous works of de Swart, McNamee and Chilton and play practical roles in current ongoing strange flavor hadron physics research. To this end, we pedagogically study the SU(3) Lie algebra, its spin symmetries, and its eigenvalues for irreducible representations. We also evaluate the values of the Wigner D functions related to the isoscalar factors; these functions are immediately applicable to strange flavor hadron phenomenology. Exploiting these SU(3) group properties associated with the spin symmetries, we investigate the decuplet-to-octet transition magnetic moments and the baryon octet and decuplet magnetic moments in the flavor symmetric limit to construct the Coleman-Glashow-type sum rules.

Study of hyperon-pion resonances from kaonic absorption with KLOE

Through the study of the absorptions of low momentum kaons in light target ( 4 He and 12 C), aspects of the hyperon-nucleon interaction in medium are investigated with the KLOE drift chamber with almost full acceptance.The in-medium modification of hadron properties is the main field of study for the strangeness sector in the non-perturbative regime of the low energy region of QCD. The behaviour of strange hadrons at extreme densities are of capital importance for the description of the nuclear equation of state and the evaluation of the strangeness component in the core of the neutron stars.The study of the antiK-hadron interactions inside the drift chamber of KLOE was initiated in order to search for signals from the formation of deeply bound kaonic nuclear states and the study of resonances like the Λ(1405) and the Σ(1385), and constitute a first step towards the preparation of the AMADEUS experiment at DAFNE, the e + e − collider of the Frascati National Laboratories (Italy) of INFN.

Particle correlations and their implication to collectivity in pPb and PbPb from CMS

The long-range two-particle correlation functions reveal the near-side ridge structures in highmultiplicity pp, pPb and PbPb collisions at the Large Hadron Collider (LHC). The model that takes into account the collective flow originated from the initial-state geometry fluctuation can successfully describe the measured long-range correlation functions of charged particles. In this review paper, the recent experimental data on the long-range correlations and the extracted elliptic and triangular flow parameters in pPb and PbPb collisions from the Compact Muon Solenoid (CMS) experiment are summarized. The flow parameters from the longrange correlation analyses are compared with those from the multiparticle cumulants and the Lee-Yang Zeros (LYZ) method. In addition, the pseudorapidity dependence of long-range two-particle correlation functions in pPb and the deduced flow parameters for identified strange hadrons (K S 0 and Λ/Λ) in pPb and PbPb are also presented to provide more insights on the long-range correlations and flow dynamics.

Strangeness Production in Deep-Inelastic ep Scattering at HERA

The production of neutral strange hadrons is studied using deep-inelastic events measured with the H1 detector at HERA. The measurements of K s 0 and Λ(Λ) productions are made in two regions of phase space defined by the negative

Deep sub-thresholdΞandΛproduction in nuclear collisions with the UrQMD transport model

We present results on deep sub-threshold hyperon production in nuclear collisions, with the UrQMD transport model. Introducing anti-$\text{kaon}+\text{baryon}$ and hyperon + hyperon strangeness exchange reactions we obtain a good description of experimental data on single strange hadron production in $\text{Ar}+\text{KCl}$ reactions at ${E}_{\mathrm{lab}}=1.76A$ GeV. We find that the hyperon strangeness exchange is the dominant process contributing to the ${\ensuremath{\Xi}}^{\ensuremath{-}}$ yield; however, our study remains short of explaining the ${\ensuremath{\Xi}}^{\ensuremath{-}}/\ensuremath{\Lambda}$ ratio measured with the HADES experiment. We also discuss possible reasons for the discrepancy with previous studies and the experimental results, finding that many details of the transport simulation may have significant effects on the final ${\ensuremath{\Xi}}^{\ensuremath{-}}$ yield.

Strangeness Production at LHC energies as measured with ALICE

The main objective of the ALICE experiment is to study the properties and the evolution of the high-energy density system created in relativistic heavy-ion collisions at the LHC. For that purpose, ALICE has unique particle identification capabilities that enable the detection of weakly-decaying particles in the high-multiplicity environment created in lead-lead (Pb-Pb) collisions.In this work, we discuss the systematic measurements of strange and multi-strange hadrons performed by ALICE for proton-proton (pp), proton-lead (p-Pb) and Pb-Pb collisions. Production rates measured for p-Pb and Pb-Pb are compared to predictions from statistical hadronization models and to measurements performed in pp collisions. These data are also used for a brief discussion on strangeness enhancement.

Transverse-momentum spectra of strange particles produced in Pb + Pb collisions atsNN=2.76TeV in the chemical nonequilibrium model

We analyze the transverse-momentum spectra of strange hadrons produced in Pb + Pb collisions at the collision energy $\sqrt{{s}_{\mathrm{NN}}}=2.76$ TeV for different centrality bins. Our approach combines the concept of chemical nonequilibrium with the single-freeze-out scenario. The two ideas are realized in the framework of the Cracow model, whose thermodynamic parameters have been established in earlier studies of the ratios of hadron multiplicities. The geometric parameters of the model are obtained from the fit to the spectra of pions and kaons, only. Using these parameters, we obtain an excellent description of the spectra of protons and the ${K}_{S}^{0},{K}^{*}{(892)}^{0}$, and $\ensuremath{\phi}(1020)$ mesons. A satisfactory description is obtained for the $\ensuremath{\Lambda},\ensuremath{\Xi}$, and $\ensuremath{\Omega}$ hyperons.

Separate Chemical Freeze-Out of Strange Particles with Conservation Laws

The Hadron Resonance Gas Model with two freeze-outs connected by the conservation laws is considered. We are arguing that the chemical freeze-out of strange hadrons should occur earlier than the chemical freeze-out of non-strange hadrons. The hadron multiplicities measured in the heavy ion collisions for the center-of-mass energy range 2.7–200GeV are described well by such a model. Based on a success of such an approach, a radical way to improve the Hadron Resonance Gas Model performance is suggested. Thus, we suggest to identify the hadronic reactions that freeze-out noticeably earlier or later that most of the others reactions (for different collision energies they may be different) and to consider a separate freeze-out for them.

Hadronic equation of state and speed of sound in thermal and dense medium

The equation of state p(ϵ) and speed of sound squared [Formula: see text] are studied in grand canonical ensemble of all hadron resonances having masses ≤2 GeV . This large ensemble is divided into strange and non-strange hadron resonances and furthermore to pionic, bosonic and fermionic sectors. It is found that the pions represent the main contributors to [Formula: see text] and other thermodynamic quantities including the equation of state p(ϵ) at low temperatures. At high temperatures, the main contributions are added in by the massive hadron resonances. The speed of sound squared can be calculated from the derivative of pressure with respect to the energy density, ∂p/∂ϵ, or from the entropy-specific heat ratio, s/cv. It is concluded that the physics of these two expressions is not necessarily identical. They are distinguishable below and above the critical temperature Tc. This behavior is observed at vanishing and finite chemical potential. At high temperatures, both expressions get very close to each other and both of them approach the asymptotic value, 1/3. In the hadron resonance gas (HRG) results, which are only valid below Tc, the difference decreases with increasing the temperature and almost vanishes near Tc. It is concluded that the HRG model can very well reproduce the results of the lattice quantum chromodynamics (QCD) of ∂p/∂ϵ and s/cv, especially at finite chemical potential. In light of this, energy fluctuations and other collective phenomena associated with the specific heat might be present in the HRG model. At fixed temperatures, it is found that [Formula: see text] is not sensitive to the chemical potential.

Recent lattice QCD results and phase diagram of strongly interacting matter

I review recent lattice QCD results on a few selected topics which are relevant to the heavy ion physics community. Special emphasis is put on the QCD equation of state at vanishing and nonzero baryon chemical potential, the onset of deconfinement of open strange and charmed hadrons, the contribution from experimentally not yet observed hadrons to the thermodynamics of the hadronic gas and their influence on freeze-out conditions of strange and light-quark hadrons.

Evidence for experimentally unobserved strange hadrons from QCD thermodynamics and their impact on freeze-out parameter

We analyze the influence of experimentally not yet observed strange hadrons – predicted by quark model calculations as well as lattice QCD – on QCD bulk thermodynamics. By comparing lattice QCD results of various combinations of net strangeness fluctuations to hadron resonance gas (HRG) model calculations with different strange hadron content, we find evidence for such additional hadronic states from QCD thermodynamics. We further investigate the impact of such states on the freeze-out parameter in heavy ion collisions. We show that the freeze-out temperature as determined from yields of strange baryons over anti-baryons is, in agreement with lattice QCD, lowered by 5–8 MeV in comparison with the conventional HRG model calculations.

Production of light nuclei in heavy-ion collisions within a multiple-freezeout scenario

We discuss the production of light nuclei in heavy ion collisions within a multiple freezeout scenario. Thermal parameters extracted from the fits to the observed hadron yields are used to predict the multiplicities of light nuclei. Ratios of strange to nonstrange nuclei are found to be most sensitive to the details of the chemical freezeout. The well-known disagreement between data of ${}_{\ensuremath{\Lambda}}^{3}\text{H}{/}^{3}\text{He}$ and $\overline{{}_{\ensuremath{\Lambda}}^{3}\text{H}{/}^{3}\text{He}}$ at $\sqrt{{s}_{NN}}=200$ GeV and models based on thermal as well as simple coalescence using a single chemical freezeout surface goes away when we let the strange and nonstrange hadrons freeze out at separate surfaces. At the CERN Large Hadron Collider energy of $\sqrt{{s}_{NN}}=2700$ GeV, multiple freezeout scenario within a thermal model provides a consistent framework to describe the yields of all measured hadrons and nuclei.

Long range two-particle correlations with Ks0 and Λ in pPb collisions

Abstract Measurements of two-particle angular correlations between identified strange hadrons ( K s 0 and Λ / Λ ¯ ) and unidentified charged particles, produced in pPb collisions, are presented over a wide range in pseudorapidity and full azimuth. Results are based on an integrated luminosity of approximately 35 nb − 1 collected during the 2013 LHC pPb run at a nucleon–nucleon center-of-mass energy of 5.02 TeV by the CMS experiment. K s 0 and Λ / Λ ¯ are reconstructed via the topology of their secondary decays. The observed long-range correlations of K s 0 and Λ / Λ ¯ are characterized by the second-order ( v 2 ) and third-order ( v 3 ) anisotropy harmonics, which are presented as a function of particle multiplicity and transverse momentum. Particle-species dependence of v 2 and v 3 is observed in a wide range of multiplicities in pPb events. Constituent quark scaling is observed within 10–15% for each multiplicity class for the v 2 and v 3 harmonics of K s 0 and Λ / Λ ¯ as a function of kinetic energy per quark.

Light-front holographic QCD and color confinement

One of the most fundamental problems in Quantum Chromodynamics is to understand the origin of the mass scale which controls the range of color confinement and the hadronic spectrum. For example, if one sets the Higgs couplings of quarks to zero, then no mass parameters appear in the QCD Lagrangian, and the theory is conformal at the classical level. Nevertheless, hadrons have a finite mass. We show that a mass gap and a fundamental color confinement scale arise when one extends the formalism of de Alfaro, Fubini and Furlan (dAFF) to frame-independent light-front Hamiltonian theory. Remarkably, the resulting light-front potential has a unique form of a harmonic oscillator in the light-front invariant impact variable if one requires that the action remains conformally invariant. The result is a single-variable relativistic equation of motion for [Formula: see text] bound states, a "Light-Front Schrödinger Equation," analogous to the nonrelativistic radial Schrödinger equation, which incorporates color confinement and other essential spectroscopic and dynamical features of hadron physics, including a massless pion for zero quark mass and linear Regge trajectories with the same slope in the radial quantum number and orbital angular momentum. The same light-front equations with the correct hadron spin dependence arise from the holographic mapping of "soft-wall model" modification of AdS5 space with a specific dilaton profile. The corresponding light-front Dirac equation provides a dynamical and spectroscopic model of nucleons. A fundamental mass parameter κ appears, determining the hadron masses and the length scale which underlies hadron structure. Quark masses can be introduced to account for the spectrum of strange hadrons. This Light-Front Holographic approach predicts not only hadron spectroscopy successfully, but also hadron dynamics — hadronic form factors, the QCD running coupling at small virtuality, the light-front wavefunctions of hadrons, ρ electroproduction, distribution amplitudes, valence structure functions, etc. Thus the combination of light-front dynamics, its holographic mapping to gravity in a higher-dimensional space and the dAFF procedure provides new insight into the physics underlying color confinement, chiral invariance, and the QCD mass scale, among the most profound questions in physics.

Additional strange hadrons from QCD thermodynamics and strangeness freezeout in heavy ion collisions.

We compare lattice QCD results for appropriate combinations of net strangeness fluctuations and their correlations with net baryon number fluctuations with predictions from two hadron resonance gas (HRG) models having different strange hadron content. The conventionally used HRG model based on experimentally established strange hadrons fails to describe the lattice QCD results in the hadronic phase close to the QCD crossover. Supplementing the conventional HRG with additional, experimentally uncharted strange hadrons predicted by quark model calculations and observed in lattice QCD spectrum calculations leads to good descriptions of strange hadron thermodynamics below the QCD crossover. We show that the thermodynamic presence of these additional states gets imprinted in the yields of the ground-state strange hadrons leading to a systematic 5-8MeV decrease of the chemical freeze-out temperatures of ground-state strange baryons.

Recent results on strangeness production at STAR

We report on the measurements of strange hadrons (K±, K0S, Λ, Ξ, Ω and ϕ) production at mid-rapidity in Au+Au collisions at = 7.7 - 39 GeV from the STAR beam energy scan (BES) program. The collision energy dependence of strange hadron yields are presented. The strange hadron related particle ratios are compared with calculations from statistical and hadronic cascade models. The nuclear modification factors and baryon to meson ratios (/K0S and Ω/ϕ) are presented. The physics implications for collision dynamics are discussed.