Multi-strange Baryon Research Articles

Multiplicity-dependent production of Σ(1385)± and Ξ(1530)0 in pp collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV

The production yields of the Σ(1385)± and Ξ(1530)0 resonances are measured in pp collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV with ALICE. The measurements are performed as a function of the charged-particle multiplicity ⟨dNch/dη⟩, which is related to the energy density produced in the collision. The results include transverse momentum (pT) distributions, pT-integrated yields, mean transverse momenta of Σ(1385)± and Ξ(1530)0, as well as ratios of the pT-integrated resonance yields relative to yields of other hadron species. The Σ(1385)±/π± and Ξ(1530)0/π± yield ratios are consistent with the trend of the enhancement of strangeness production from low to high multiplicity pp collisions, which was previously observed for strange and multi-strange baryons. The yield ratio between the measured resonances and the long-lived baryons with the same strangeness content exhibits a hint of a mild increasing trend at low multiplicity, despite too large uncertainties to exclude the flat behaviour. The results are compared with predictions from models such as EPOS-LHC and PYTHIA 8 with Rope shoving. The latter provides the best description of the multiplicity dependence of the Σ(1385)± and Ξ(1530)0 production in pp collisions at s\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$ \\sqrt{s} $$\\end{document} = 13 TeV.

Centrality dependence of multistrange baryon production in high-energy heavy-ion collisions

We consider the experimental data on the production of strange \Lambda^{\prime}Λ′s, and multistrange baryons (\XiΞ, \OmegaΩ), and antibaryons, on nuclear targets, at the energy region from SPS up to LHC, in the framework of the Quark-Gluon String Model. One remarkable result of this analysis is the significant dependence on the centrality of the collision of the experimental \overline{\Xi}^+/\overline{\Lambda}Ξ¯+/Λ¯ and \overline{\Omega}^+/\overline{\Lambda}Ω¯+/Λ¯ ratios in heavy-ion collisions, at SPS energies.

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.

Multistrange hyperon production on nuclear targets

We consider the experimental data on yields of protons, strange $\Lambda^{\prime}$s, and multistrange baryons ($\Xi$, $\Omega$), and antibaryons production on nuclear targets, and the experimental ratios of multistrange to strange antibaryon production, at the energy region from SPS up to LHC, and compare them to the results of the Quark-Gluon String Model calculations. In the case of heavy nucleus collisions, the experimental dependence of the $\overline{\Xi}^+/\overline{\Lambda}$, and, in particular, of the $\overline{\Omega}^+/\overline{\Lambda}$ ratios, on the centrality of the collision, shows a manifest violation of quark combinatorial rules.

Probing CP symmetry and weak phases with entangled double-strange baryons

Though immensely successful, the standard model of particle physics does not offer any explanation as to why our Universe contains so much more matter than antimatter. A key to a dynamically generated matter–antimatter asymmetry is the existence of processes that violate the combined charge conjugation and parity (CP) symmetry1. As such, precision tests of CP symmetry may be used to search for physics beyond the standard model. However, hadrons decay through an interplay of strong and weak processes, quantified in terms of relative phases between the amplitudes. Although previous experiments constructed CP observables that depend on both strong and weak phases, we present an approach where sequential two-body decays of entangled multi-strange baryon–antibaryon pairs provide a separation between these phases. Our method, exploiting spin entanglement between the double-strange Ξ− baryon and its antiparticle2{bar{{Xi }}}^{+}, has enabled a direct determination of the weak-phase difference, (ξP − ξS) = (1.2 ± 3.4 ± 0.8) × 10−2 rad. Furthermore, three independent CP observables can be constructed from our measured parameters. The precision in the estimated parameters for a given data sample size is several orders of magnitude greater than achieved with previous methods3. Finally, we provide an independent measurement of the recently debated Λ decay parameter αΛ (refs. 4,5). The {Lambda }bar{{Lambda }} asymmetry is in agreement with and compatible in precision to the most precise previous measurement4.

Strange particle production in jets and underlying events in pp collisions at $$\sqrt{s} = 7$$ TeV with PYTHIA8 generator

Strange hadron production in pp collisions at $\sqrt{s}~=~7$ TeV is studied in jets and underlying events using the PYTHIA8 event generator. Matching strange hadrons to the jet area and the underlying event area is expected to help us disentangle the strange particles produced in hard and soft processes. The yield and the relative production of strange hadrons dependent on the event multiplicity are investigated with the color reconnection and color rope mechanisms implemented in the PYTHIA8 framework. It is found that the inclusive strange hadron productions can be reasonably described by the color reconnection and color rope combined effects. A significant multiplicity dependent enhancement of the strange baryon production in the jet area is observed induced by the modified string fragmentation mechanisms, indicating the strange baryon enhancement persists in both the hard and the soft process. Multi-strange baryons are found to be more collimated with the jet axis than other strange hadrons in the string fragmentation picture with the jet shape analysis technique. Future experimental examination of these jet related strange hadron productions will provide more insight to the origin of strangeness enhancement in small systems.

Centrality dependence of multistrangeness production in high-energy heavy-ion collisions

We compare the experimental data on yields of protons, strange Λ′s, and multistrange baryons (Ξ, Ω), and antibaryons production on nuclear targets, and the experimental ratios of multistrange to strange antibaryon production, at the energy region from SPS up to LHC, with the corresponding results of the Quark-Gluon String Model calculations. In the case of heavy nucleus collisions, the experimental dependence of the Ξ̅+/Λ̅, and Ω̅+/Λ̅ ratios, on the centrality of the collision, shows a manifest violation of quark combinatorial rules.

Event-shape studies of strangeness production in √S = 13 TeV proton–proton collisions with ALICE

The ALICE Collaboration has observed that the relative fraction of strange hadrons grows strongly with multiplicity in small collision systems at LHC energies, in particular for multi-strange baryons. The origin of this effect is still under debate, and models need significant final-state interactions to accommodate the new ALICE results, requiring new tools to discriminate experimentally between the various phenomenological ideas. In these proceedings we present a multi-differential study of identified particle spectra with respect to the event multiplicity and two different event shape observables, the unweighted transverse spherocity SOpT=1, and the self-normalized, transverse charged particle density, RT, which allows us to explore particle production associated with hard and soft QCD processes. ALICE has measured π, K, ϕ, and Ξ production at mid-rapidity (|η| < 0.8) as a function of SOpT=1 and RT in pp collisions at √S = 13 TeV. This work reports on how these multi-differential measurements compare with predictions from PYTHIA and EPOSLHC.

Theoretical analysis of pT spectra of light-flavor hadrons in p + p collisions at s = 7 TeV under differential and single freeze-out scenarios

We present the published data of ALICE at mid-rapidity region ([Formula: see text]) to study the [Formula: see text] spectra of light-flavor hadrons in different charged-particle multiplicities ([Formula: see text]) for [Formula: see text] collisions at [Formula: see text] TeV. We parametrize the [Formula: see text] spectra of different hadrons such as pion ([Formula: see text]), kaon ([Formula: see text]), [Formula: see text], [Formula: see text] ([Formula: see text]), [Formula: see text], proton ([Formula: see text]), lambda ([Formula: see text]), cascade ([Formula: see text]) and omega ([Formula: see text]) using Tsallis distribution. We perform this analysis by considering both differential and single freeze-out scenarios. In the differential freeze-out scenario, both the Tsallis parameters [Formula: see text] and [Formula: see text] increase with charged multiplicities for most of the particles. This implies that the multipartonic interactions increase the multiplicities in [Formula: see text] collisions and it brings the system towards thermal equilibrium. Here we observe that both [Formula: see text] and [Formula: see text] have different trends with different masses of particles. The parameters [Formula: see text] and [Formula: see text] are higher for massive particles (except for multistrange baryons) in comparison to lighter ones, which supports the differential freeze-out scenario and suggests that massive particles freeze-out earlier from the system. In the case of single freeze-out scenario, the value of parameter [Formula: see text] has a little variation with multiplicity and the parameter [Formula: see text] increases with multiplicity. This implies that the degree of thermalization remains similar for the events of different multiplicity classes.

Performance of the MPD Detector for the Study of Multi-strange Baryon Production in Heavy-ion Collisions at the Nuclotron-based Ion Collider Facility (NICA)

Presented are selected results of the Multi-Purpose Detector (MPD) for reconstruction of  and -baryons and K0-mesons in a Monte Carlo simulation of heavy-ion collisions at the Nuclotron-based Ion Collider fAcility (NICA). The results were obtained from the full MPD simulation and reconstruction chain, and include yields, spectra, and anisotropy coefficients from the centrality selected Au+Au collisions.

Probing strangeness production in small systems through new multi-differential measurements with ALICE at the LHC

ALICE has observed that the relative fraction of strange hadrons grows strongly with multiplicity in small collision systems (proton-proton and proton-lead collisions) at LHC energies, in particular for multi-strange baryons. This implies that a proton-proton collision cannot be described as an incoherent sum of parton-parton collisions, an idea that has been central in most proton-proton generators, for example PYTHIA.To accommodate the new ALICE results, models have to introduce significant final-state interactions. These final-state effects can have very different phenomenological origin. To be able to eventually discriminate experimentally between different final-state models, new experimental tools are required and in this paper different multi-differential observables will be tested with this goal in mind. Transverse Spherocity (SO ) is an observable that allows a topological selection of events that are “isotropic” (dominated by multiple soft processes) and “jetty” (where a single hard process is responsible for a significant part of the multiplicity). The underlying event activity is another observable that can be used to vary the amount of soft processes. It can be estimated by measuring the charged-particle multiplicity in the Transverse region (RT ).Using these new observables, ALICE has obtained results for π, K, φ, p, and production at mid-rapidity as a function of event shape and underlying event activity in proton-proton collisions at . Finally, this contribution will report on how these new multi-differential measurements compare to predictions from PYTHIA and EPOS-LHC.

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.

First Observation of an Attractive Interaction between a Proton and a Cascade Baryon.

This Letter presents the first experimental observation of the attractive strong interaction between a proton and a multistrange baryon (hyperon) Ξ^{-}. The result is extracted from two-particle correlations of combined p-Ξ^{-}⊕p[over ¯]-Ξ[over ¯]^{+} pairs measured in p-Pb collisions at sqrt[s_{NN}]=5.02 TeV at the LHC with ALICE. The measured correlation function is compared with the prediction obtained assuming only an attractive Coulomb interaction and a standard deviation in the range [3.6, 5.3] is found. Since the measured p-Ξ^{-}⊕p[over ¯]-Ξ[over ¯]^{+} correlation is significantly enhanced with respect to the Coulomb prediction, the presence of an additional, strong, attractive interaction is evident. The data are compatible with recent lattice calculations by the HAL-QCD Collaboration, with a standard deviation in the range [1.8, 3.7]. The lattice potential predicts a shallow repulsive Ξ^{-} interaction within pure neutron matter and this implies stiffer equations of state for neutron-rich matter including hyperons. Implications of the strong interaction for the modeling of neutron stars are discussed.

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.

Enhancement of strange baryons in high-multiplicity proton–proton and proton–nucleus collisions

Abstract We investigate the enhancement of yields of strange and multi-strange baryons in proton–proton (p+p), proton–lead (p+Pb), and lead–lead (Pb+Pb) collisions at Large Hadron Collider (LHC) energies from a dynamical core–corona initialization model. We first generate partons just after the collisions by using event generators. These partons dynamically generate the quark gluon plasma (QGP) fluids through the source terms in the hydrodynamic equations. According to the core–corona picture, this process tends to happen where the density of generated partons is high and their transverse momentum is low. Some partons do not fully participate in this process when they are in dilute regions or their transverse momentum is high, and subsequently fragment into hadrons through string fragmentation. In this framework, the final hadrons come from either chemically equilibrated fluids as in the conventional hydrodynamic models or string fragmentation. We calculate the ratio of strange baryons to charged pions as a function of multiplicity and find that it monotonically increases up to $dN_{\mathrm{ch}}/d\eta \sim 100$ and then saturates above. This suggests that the QGP fluids are partly created and that their fraction increases with multiplicity in p+p and p+Pb collisions at LHC energies.

Improved quark coalescence for a multi-phase transport model

The string melting version of a multi-phase transport model is often applied to high-energy heavy-ion collisions since the dense matter thus formed is expected to be in parton degrees of freedom. In this work we improve its quark coalescence component, which describes the hadronization of the partonic matter to a hadronic matter. We removed the previous constraint that forced the numbers of mesons, baryons, and antibaryons in an event to be separately conserved through the quark coalescence process. A quark now could form either a meson or a baryon depending on the distance to its coalescence partner(s). We then compare results from the improved model with the experimental data on hadron $dN/dy$, $p_{_{\rm T}}$ spectra, and $v_2$ in heavy-ion collisions from $\sqrt{s_{_{\rm NN}}}=62.4$ GeV to $5.02$ TeV. We show that, besides being able to describe these observables for low-$p_{_{\rm T}}$ pions and kaons, the improved model also better describes the low-$p_{_{\rm T}}$ baryon observables in general, especially the baryon $p_{_{\rm T}}$ spectra and antibaryon-to-baryon ratios for multistrange baryons.

Light flavour hadron production in pp collisions at = 13 TeV with ALICE

The ALICE detector has excellent Particle IDentification (PID) capabilities in the central barrel (|η| < 0.9). This allows identified hadron production to be measured over a wide transverse momentum (pT) range, using different sub-detectors and techniques: their specific energy loss (dE/dx), the velocity determination via time-of-flight measurement, the Cherenkov angle or their characteristic weak decay topology. Results on identified light flavour hadron production at mid-rapidity measured by ALICE in proton-proton collisions at = 13 TeV are presented and compared with previous measurements performed at lower energies. The results cover a wide range of particle species including long-lived hadrons, resonances and multi-strange baryons over the pT range from 150 MeV/c up to 20 GeV/c, depending on the particle species.

Strangeness in STAR experiment at RHIC

We present the recent results of strangeness production at the mid-rapidity in Au + Au collisions at RHIC, from to 200 GeV. Elliptic asymmetry v2 of multi-strange baryon Ω and φ mesons are similar to that of pions and protons in the intermediate pT range (2 - 5 GeV/c) in GeV Au + Au collisions, indicating that the major part of collective ow has been built up at partonic stage. The breaking of mass ordering between φ mesons and protons in the low pT range (< 1 GeV/c) is consistent with a picture that φ mesons are less sensitive to later hadronic interaction. The nuclear modification factor RCP and baryon to meson ratio change dramatically when the collision energy is lower than 19.6 GeV. It suggests a possible change of the created QCD medium properties at lower energies compared to those from high energies.

Strangeness in ALICE at the LHC

Strangeness production has been measured by the ALICE experiment in different collision systems at the unprecedented center-of-mass energies available at the CERN Large Hadron Collider. In Pb–Pb collisions at TeV the relative production of strange and multi-strange baryons relative to pions is observed to follow a saturating trend with increasing centrality, and reaching values that are consistent with those predicted by thermal model calculations in the Grand-Canonical ensemble. More recently, the multiplicity dependence of strangeness production in small systems such as pp and p–Pb has also been investigated. An overview of the most recent results on strangeness production is reported, including the first observation of strangeness enhancement with charged particle multiplicity in pp collisions.

Light flavor results in p–Pb collisions with ALICE

Particle ratios provide insight into the hadrochemistry of the event and the mechanisms for particle production. In Pb-Pb collisions the relative multi-strange baryon yields exhibit an enhancement with respect to pp collisions, whereas the short-lived K*0 resonance is suppressed in the most central events due to re-scattering of its decay daughter particles. Measurements in p-Pb allow us to investigate the development of these effects as a function of the system size.We report comprehensive results on light-flavor hadron production measured with the ALICE detector in p-Pb collisions at sNN=5.02 TeV, covering a wide range of particle species which includes long-lived hadrons, resonances and multi-strange baryons. The measurements include the transverse momentum spectra and the ratios of spectra among different species, and extend over a very large transverse momentum region, from ≈100 MeV/c to ≈20 GeV/c, depending on the particle species.