Multi-strange Hadrons Research Articles

Universality in hadronic and nuclear collisions at high energy

Recent experimental results in proton-proton and in proton-nucleus collisions at Large Hadron Collider energies show a strong similarity to those observed in nucleus-nucleus collisions, where the formation of a quark-gluon plasma is expected. We discuss the comparison between small colliding systems and nucleus-nucleus collisions, for: a)~the strangeness suppression factor $\gamma_s$ and yields of multi-strange hadrons; b)~the average transverse momentum, $p_t$, with particular attention to the low $p_t$ region where soft, non-perturbative effects are important; c)~the elliptic flow scaled by the participant eccentricity. The universal behavior in hadronic and nuclear high energy collisions emerges for all these observables in terms of a specific dynamical variable which corresponds to the entropy density of initial system in the collision and which takes into account the transverse size of the initial configuration and its fluctuations.

Multiplicity dependence of strange and multi-strange hadrons in p–p, p–Pb and Pb–Pb collisions at LHC energies using Tsallis–Weibull formalism

The transverse momentum ($p_{T}$) distribution of strange hadrons ($K_{S}^{0}$ and $\Lambda$) and multi-strange hadrons( $\Xi$ and $\Omega$) measured in p$-$p, p$-$Pb, and Pb$-$Pb collisions at LHC energies have been studied for different multiplicity classes using Tsallis-Weibull (or q$-$Weibull)formalism. The distribution describes the measured $p_{T}$ spectra for all multiplicity (or centrality)classes. The multiplicity dependence of the extracted parameters are studied for the mentioned collisions systems. The $\lambda$ parameter was observed to increase systematically with the collision multiplicity and follows a mass hierarchy for all collision system. This characteristic feature indicates that $\lambda$ can be associated to the strength of collectivity for heavy ion collisions. It can also be related to strength of dynamic effects such as multi-partonic interactions and color reconnections which mimic collectivity in smaller systems. The non-extensive $q$ parameter is found to be greater than one for all the particles suggesting that the strange particles are emitted from a source which is not fully equilibrated.

Monte-Carlo study of long-range correlations of average transverse momentum and multiplicity for strange particles in pp-collisions at the LHC energies

This study is motivated by the puzzling enhanced production of multi-strange hadrons observed for the first time by the ALICE Collaboration in high-multiplicity pp-collisions at at the LHC. We investigate this effect of strangeness enhancement in pp-collisions in the framework of the MC event generator PYTHIA 8 where the collectivity processes are taken into account by the formation of a so-called flavour rope. The latter is hadronized with a larger effective string tension providing the increase of strangeness yield. This concept of the flavour rope, as a source of multi-strange hadrons, extended in rapidity, is being tested by the study of so called long-range correlations (LRC) between the average transverse momentum 〈pT〉 and multiplicity n for charged particles containing strange quarks produced in high energy pp-collisions.The dependencies of correlation coefficients bn−n, bPT−n and bPT−PT on the gap between forward and backward pseudorapidity windows, and on the width of the forward pseudorapidity windows, are studied and the results are discussed.

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.

Multiplicity dependence of strangeness and hadronic resonance production in pp and p-Pb collisions with ALICE at the LHC

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 sNN=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 multi-strange hadron production in pp collisions at s=13TeV with ALICE. We also presented recent measurements of mesonic and baryonic resonances in small collision systems like pp and p–Pb at sNN=13 and 8.16 TeV, respectively. The multiplicity dependent studies in pp and p-Pb collisions have been used to investigate how the hadronic scattering processes affect measured resonance yields and to better understand the interplay between canonical suppression and strangeness enhancement. The measurement of the ϕ(1020) meson as a function of multiplicity provides crucial constraints in this context.

Performance Studies for Strange Hadron Flow Measurements in CBM at FAIR

Measurements of the directed and elliptic flow of strange and multi-strange hadrons are an important part of the physics program of the Compressed Baryonic Matter experiment (CBM) at the future accelerator complex FAIR in Darmstadt, Germany. We present recent results from the CBM performance studies for measurements of the directed (

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.

Strange hadron production in pp, pPb, and PbPb collisions at LHC energies

Identified particle spectra provide an important tool for understanding the particle production mechanism and the dynamical evolution of the medium created in relativistic heavy ion collisions. Studies involving strange and multi-strange hadrons, such as K0S, Λ, and Ξ−, carry additional information since there is no net strangeness content in the initial colliding system. Strangeness enhancement in AA collisions with respect to pp and pA collisions has long been considered as one of the signatures for quark-gluon plasma (QGP) formation. Recent observations of collective effects in high-multiplicity pp and pA collisions raise the question of whether QGP can also be formed in the smaller systems. Systematic studies of strange particle abundance, particle ratios, and nuclear modification factors can shed light on this issue. The CMS experiment has excellent strange-particle reconstruction capabilities over a broad kinematic range, and dedicated high-multiplicity triggers in pp and pPb collisions. The spectra of K0S, Λ, and Ξ− hadrons have been measured in various multiplicity and rapidity regions as a function of pT in pp, pPb, and PbPb collisions for several collision energies. The spectral shapes and particle ratios are compared in the different collision systems for events that have the same multiplicity and interpreted in the context of hydrodynamics models.

Nuclear modification of light flavour and strangeness at LHC energies with ALICE

Thanks to its unique particle identification capabilities the ALICE detector is able to identify light-flavour, strange and multi-strange hadrons, including π, K, p, , Λ, Ξ and Ω, over a wide range of transverse momentum, from pp and p–Pb interactions up to central Pb–Pb collisions. The latest results on the nuclear modification factor, RAA, as a function of the Pb–Pb collision centrality, is shown for various particle specie at centre-of-mass energy. For each particle specie, the RAA is compared with the nuclear modification factors RpA in p-Pb collisions to asses the presence of hot nuclear matter effects affecting the high-pΤ particle production in Pb–Pb collisions. The results on the RAA of charged hadrons at , the highest energy ever reached in the laboratory for heavy-ion collisions, is also shown.

Hydrodynamic predictions for Pb+Pb collisions at 5.02 TeV

Predictions and comparisons of hadronic flow observables for Pb+Pb collisions at 2.76 A TeV and 5.02 A TeV are presented using a hydrodynamics + hadronic cascade hybrid approach. Initial conditions are generated via a new formulation of the IP-Glasma model and then evolved using relativistic viscous hydrodynamics and finally fed into transport cascade in the hadronic phase. The results of this work show excellent agreement with the recent charged hadron anisotropic flow measurements from the ALICE collaboration of Pb+Pb collisions at 5.02 A TeV. Event-by-event distributions of charged hadron v n , flow event-plane correlations, and flow factorization breaking ratios are compared with existing measurements at 2.76 A TeV, and are predicted at 5.02 A TeV. Further predictions of identified hadron observables (for both light and multi-strange hadrons), such as p T -spectra and anisotropic flow coefficients, are presented.

Enhanced production of multi-strange hadrons in high-multiplicity proton\u2013proton collisions

Quark–gluon plasma is an exotic state of matter that can emerge in heavy nuclei high-energy collisions. The ALICE collaboration reports the first observation of strangeness enhancement in proton–proton collisions, a possible signature of this state.

Multi-strange hadrons and the precision extraction of QGP properties in the RHIC-BES domain

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 and the modification to their transverse momentum spectra due to these interactions.

Violation of mass ordering for multi-strange hadrons at RHIC and LHC

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 affected by hadronic rescattering and, as a result, the mass ordering of the pT-differential elliptic flow parameter v2(pT) is violated: At the RHIC and the LHC energies the v2(pT) for ϕ-mesons is larger than that for protons in the low-pT regions.

Heavy baryonic resonances, multistrange hadrons, and equilibration at energies available at the GSI Schwerionensynchrotron, SIS18

We study the details and time dependence of particle production in nuclear collisions at a fixed target beam energy of $E_{\mathrm{lab}}= 1.76$ A GeV with the UrQMD transport model. We find that the previously proposed production mechanism for multi strange hadrons, $\phi$ and $\Xi$, are possible due to secondary interactions of incoming nuclei of the projectile and target with already created nuclear resonances, while the Fermi momenta of the nuclei play only a minor role. We also show how the centrality dependence of these particle multiplicities can be used to confirm the proposed mechanism, as it strongly depends on the number of participants in the reaction. Furthermore we investigate the time dependence of particle production in collisions of Ca+Ca at this beam energy, in order to understand the origins of the apparent chemical equilibration of the measured particle yields. We find that indeed the light hadron yields appear to be in equilibrium already from the very early stage of the collision while in fact no local equilibration, through multi collision processes, takes place. The apparent equilibrium is reached only through the decay of the resonances according to available phase space.

Centrality and Transverse Momentum Dependence of Elliptic Flow of Multistrange Hadrons and ϕ Meson in Au+Au Collisions at √[sNN]=200 GeV.

We present high precision measurements of elliptic flow near midrapidity (|y|<1.0) for multistrange hadrons and ϕ meson as a function of centrality and transverse momentum in Au+Au collisions at center of mass energy √[sNN]=200 GeV. We observe that the transverse momentum dependence of ϕ and Ω v2 is similar to that of π and p, respectively, which may indicate that the heavier strange quark flows as strongly as the lighter up and down quarks. This observation constitutes a clear piece of evidence for the development of partonic collectivity in heavy-ion collisions at the top RHIC energy. Number of constituent quark scaling is found to hold within statistical uncertainty for both 0%-30% and 30%-80% collision centrality. There is an indication of the breakdown of previously observed mass ordering between ϕ and proton v2 at low transverse momentum in the 0%-30% centrality range, possibly indicating late hadronic interactions affecting the proton v2.

Production of multistrange hadrons, light nuclei and hypertriton in central Au+Au collisions atsNN=11.5 and 200 GeV

The production of dibaryons, light nuclei and hypertriton in the most central Au+Au collisions at $\sqrt{s_{NN}}=$ 11.5 and 200 GeV are investigated by using a naive coalescence model. The production of light nuclei is studied and found that the production rate reduces by a factor of 330 (1200) for each extra nucleon added to nuclei at $\sqrt{s_{NN}}=$ 11.5 (200) GeV. The $p_{T}$ integrated yield of multistrange hadrons falls exponentially as strangeness quantum number increases. We further investigate strangeness population factor $S_{3}, S_{2}$ as a function of transverse momentum as well as $\sqrt{s_{NN}}$. The calculations for $\sqrt{s_{NN}}=$ 11.5 GeV presented here will stimulate interest to carry out these measurements during the phase-II of beam energy scan program at STAR experiment.

An Experimental Review on Elliptic Flow of Strange and Multistrange Hadrons in Relativistic Heavy Ion Collisions

Strange hadrons, especially multistrange hadrons, are good probes for the early partonic stage of heavy ion collisions due to their small hadronic cross sections. In this paper, I give a brief review on the elliptic flow measurements of strange and multistrange hadrons in relativistic heavy ion collisions at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC).

Chemical and thermal freeze-out of identified hadrons at the LHC

This proceedings contribution briefly summarizes our recent VISHNU hybrid model investigations on the chemical and thermal freeze-out of various hadrons species in 2.76 A TeV Pb+Pb collisions. Detailed analysis on the evolution of particle yields and the last elastic collisions distributions during the hadronic evolution reveals that the two multi-strange hadrons, Ξ and Ω, experience early chemical and thermal freeze-out when compared with other hadron species.

Centrality dependence of elliptic flow of multi-strange hadrons in Au+Au collisions at √sNN = 200 GeV

We present recent results of the mid-rapidity elliptic flow (ν2) for multi-strange hadrons and the ϕ meson as a function of centrality in Au + Au collisions at the center of mass energy √sNN = 200 GeV. The transverse momentum dependence of ϕ and Ω ν2 is similar to that of pion and proton, indicating that the heavier strange (s) quark flows as strongly as the lighter up (u) and down (d) quarks. These observations constitute a clear piece of evidence for the development of partonic collectivity in heavy-ion collisions at the top RHIC energy. In addition, the mass ordering of ν2 breaks between the ϕ and proton at low transverse momenta in the 0-30% centrality bin, possibly due to the effect of late hadronic interactions on the proton ν2.

Spectra and Elliptic Flow of (Multi)Strange Hadrons at RHIC and LHC within Viscous Hydrodynamics + Hadron Cascade Hybrid Model

Using the (2+1)-dimensional ultrarelativistic viscous hydrodynamics + hadron cascade,VISHNU, hybrid model, we study thepT-spectra and elliptic flow ofΛ,Ξ, andΩin Au + Au collisions atsNN= 200 GeV and in Pb + Pb collisions atsNN= 2.76 TeV. Comparing our model results with the data measurements, we find that theVISHNUmodel gives good descriptions of the measurements of these strange and multistrange hadrons at several centrality classes at RHIC and LHC. Mass ordering of elliptic flowv2amongπ,K,p,Λ,Ξ, andΩare further investigated and discussed at the two collision systems. We find that, at both RHIC and LHC,v2mass ordering amongπ,K,p, andΩis fairly reproduced within theVISHNUhybrid model, and more improvements are needed to be implemented for well describingv2mass ordering amongp,Λ, andΞ.