Strangeness Production Research Articles

Particle production at RHIC and LHC energies

The production of pion, kaon and proton was measured in Pb–Pb collisions at nucleus–nucleus center-of-mass energy [Formula: see text] by the ALICE experiment at Large Hadron Collider (LHC). The particle ratios of these species compared to the RHIC measurements are confronted to the hadron resonance gas (HRG) model and to simulations based on the event generators PYTHIA 6.4.21 and HIJING 1.36. It is found that the homogeneous particle–antiparticle ratios (same species) are fully reproducible by means of HRG and partly by PYTHIA 6.4.21 and HIJING 1.36. The mixed kaon–pion and proton–pion ratios measured at RHIC and LHC energies seem to be reproducible by the HRG model. On the other hand, the strange abundances are underestimated in both event generators. This might be originated to strangeness suppression in the event generators and/or possible strangeness enhancement in the experimental data. It is apparent that the values of kaon–pion ratios are not sensitive to the huge increase of [Formula: see text] from 200 (RHIC) to 2760 GeV (LHC). We conclude that the ratios of produced particle at LHC seem not depending on the system size.

Measuring nuclear modification factors for φ-mesons in p + Pb and Pb + Pb collisions in the ALICE experiment at the large hadron collider

Investigations of light vector mesons allow us to understand the mechanisms of hadron production in more detail and to investigate the properties of the dense and hot medium formed in central collisions of heavy ultrarelativistic nuclei. One of the most useful objects for investigations are φ-mesons, since their properties are sensitive to such effects as strangeness enhancement, the restoration of chiral symmetry, and the loss of parton energy that accompanies a phase transition. To investigate these phenomena, meson production must be measured not only in collisions of heavy nuclei but in proton-proton and proton-nuclear collisions as well. Measurements in elementary nucleon-nucleon collisions are used as the basis for comparison to heavier interacting systems. The collision of light and heavy nuclei allows us to evaluate the effects of cold nuclear matter and to interpret the effects of a hot nuclear medium more precisely. Invariant differential production spectra of φ-mesons were measured in the ALICE experiment as a function of transverse momenta in p + p, p + Pb, and Pb + Pb interactions. The distributions of the nuclear modification factors were constructed for φ-mesons on the basis of these data.

Reconstruction of multistrange hyperons with the MPD detector at the NICA collider: a Monte Carlo feasibility study

One of the main tasks of the NICA/MPD physics program is a study of strangeness production in nuclear collisions. In this paper the MPD detector performance for measurements of Λ, Ξ− and Ω− hyperons and their antiparticles \(\bar \Lambda\), \(\bar \Xi ^ +\) and \(\bar \Omega ^ +\) in central Au+Au collisions at NICA energies is presented.

Observation of Λ(4)H Hyperhydrogen by Decay-Pion Spectroscopy in Electron Scattering.

At the Mainz Microtron MAMI, the first high-resolution pion spectroscopy from decays of strange systems was performed by electron scattering off a (9)Be target in order to study the Λ binding energy of light hypernuclei. Positively charged kaons were detected by a short-orbit spectrometer with a broad momentum acceptance at 0° forward angles with respect to the beam, efficiently tagging the production of strangeness in the target nucleus. Coincidentally, negatively charged decay pions were detected by two independent high-resolution spectrometers. About 10(3) pionic weak decays of hyperfragments and hyperons were observed. The pion momentum distribution shows a monochromatic peak at pπ≈133 MeV/c, corresponding to the unique signature for the two-body decay of hyperhydrogen Λ(4)H→(4)He+π(-), stopped inside the target. Its Λ binding energy was determined to be BΛ=2.12±0.01 (stat)±0.09 (syst)MeV with respect to the (3)H+Λ mass.

Φ-meson nuclear modification factors at the lead nuclei collisions in the ALICE experiment at the LHC

Hadron spectra measurements in proton–proton and nucleus–nucleus collisions at the LHC provide the means to study the mechanisms of particle production and properties of the medium formed in relativistic heavy ion collisions. The φ-meson is a very rich probe since it is sensitive to several aspects of the collision such as strangeness enhancement, chiral symmetry restoration, and parton energy loss. Due to its small inelastic cross-section, the φ-meson is not strongly affected by the late hadronic rescattering and is sensitive to the initial evolution of the system. With a mass similar to that of the proton, it is interesting to see how the φ-meson fits within the meson/baryon pattern of observables. Being a pure ss¯ state, it further constrains the energy loss and recombination pictures. This article presents recent results on φ-meson invariant yields and nuclear modification factors measured in a wide range of transverse momentum up to 21 GeV/c2 in (p + p) and (Pb + Pb) collisions at different centralities. The proton-to-(φ-meson) yield (p/φ) ratio as a function of transverse momentum in (Pb + Pb) collisions at an energy of SNN = 2.76 TeV is also presented.

Multi-strange baryon production in pp, p–Pb and Pb–Pb collisions measured with ALICE

Transverse momentum spectra and yields of charged Ξ and Ω at mid-rapidity in pp, p-Pb and Pb-Pb collisions at the LHC have been measured by the ALICE Collaboration. These baryons are identified by reconstruction of their weak decay topology, in modes with only charged decay products, using the excellent tracking and particle identification capabilities of the detector. The recent measurements of the multi-strange baryon production relative to non-strange particles in p-Pb collisions are presented: this would help to understand the change in relative strangeness production from pp collisions to Pb-Pb collisions. Results on the nuclear modification factors for the charged Ξ and Ω particles, compared with those for other light particles, are also reported.

Strangeness production associated to a high-pT particle in Pb-Pb collisions at = 2.76 TeV with ALICE

Particle production in heavy-ion collisions at RHIC and the LHC reveals an enhancement of the baryon-to-meson ratios with respect to pp collisions. The observed suppression of high-pT particles raises the question of how the jet fragments may (re)distribute in ultra-relativistic heavy-ion collisions. With two-hadron correlations, we can study the particle composition in jets in order to get a better understanding of the aforementioned observables and the particle production mechanisms in the dense medium. In these proceedings, we present the status of the current analysis using two-hadron angular correlations for Pb-Pb collisions at = 2.76 TeV using the ALICE detector. We study the two different possibilities, considering the strange particle as either the trigger particle or the associated particle. Results on K0s-h±, (Λ A)-h± and h±-K0S correlations are shown for central collisions.

Backtracking algorithm for lepton reconstruction with HADES

The High Acceptance Di-Electron Spectrometer (HADES) at the GSI Helmholtzzentrum für Schwerionenforschung investigates dilepton and strangeness production in elementary and heavy-ion collisions. In April - May 2012 HADES recorded 7 billion Au+Au events at a beam energy of 1.23 GeV/u with the highest multiplicities measured so far. The track reconstruction and particle identification in the high track density environment are challenging. The most important detector component for lepton identification is the Ring Imaging Cherenkov detector. Its main purpose is the separation of electrons and positrons from large background of charged hadrons produced in heavy-ion collisions. In order to improve lepton identification this backtracking algorithm was developed. In this contribution we will show the results of the algorithm compared to the currently applied method for e+/-identification. Efficiency and purity of a reconstructed e+/- sample will be discussed as well.

Reconstruction of π0 and η mesons via conversion method in Au+Au at 1.23 GeV/u with HADES

Lepton pairs emerging from decays of virtual photons represent promising probes of matter under extreme conditions. In the energy domain of 1 - 2 GeV per nucleon, the HADES experiment at GSI Helmholtzzentrum fuer Schwerionenforschung in Darmstadt studies di-electrons and strangeness production in various reactions, i.e. collisions of pions, protons, deuterons, heavy-ions, and nuceous with nuclei. An accurate determination of the medium radiation depends on a precise knowledge of the underlying hadronic cocktail composed of various sources contributing to the net spectra. Therefore, a measurement of the neutral meson yields together with the dileptons is crucial. In this contribution, the capability of HADES to detect e+e− pairs from conversion of real photons will be demonstrated. We will present results from a two-photon analysis of Au+Au collisions at 1.23 GeV/u providing information on neutral π0 and η mesons.

Effects of overlapping strings in pp collisions

In models for hadron collisions based on string hadronization, the strings are usually treated as independent, allowing no interaction between the confined colour fields. In studies of nucleus collisions it has been suggested that strings close in space can fuse to form “colour ropes”. Such ropes are expected to give more strange particles and baryons, which also has been suggested as a signal for plasma formation. Overlapping strings can also be expected in pp collisions, where usually no phase transition is expected. In particular at the high LHC energies the expected density of strings is quite high. To investigate possible effects of rope formation, we present a model in which strings are allowed to combine into higher multiplets, giving rise to increased production of baryons and strangeness, or recombine into singlet structures and vanish. Also a crude model for strings recombining into junction structures is considered, again giving rise to increased baryon production. The models are implemented in the dipsy MC event generator, using Pythia8 for hadronization, and comparison to pp minimum bias data, reveals improvement in the description of identified particle spectra.

Hawking-Unruh hadronization and strangeness production in high energy collisions

The interpretation of quark ($q$)- antiquark ($\bar q$) pairs production and the sequential string breaking as tunneling through the event horizon of colour confinement leads to a thermal hadronic spectrum with a universal Unruh temperature, $T \simeq 165$ Mev,related to the quark acceleration, $a$, by $T=a/2\pi$. The resulting temperature depends on the quark mass and then on the content of the produced hadrons, causing a deviation from full equilibrium and hence a suppression of strange particle production in elementary collisions. In nucleus-nucleus collisions, where the quark density is much bigger, one has to introduce an average temperature (acceleration) which dilutes the quark mass effect and the strangeness suppression almost disappears.

Statistical Model of the Early Stage of Nucleus--Nucleus Collisions with Exact Strangeness Conservation

The Statistical Model of the Early Stage, SMES, describes a transition between confined and deconfined phases of strongly interacting matter created in nucleus-nucleus collisions. The model was formulated in the late 1990s for central Pb+Pb collisions at the CERN SPS energies. It predicted several signals of the transition (onset of deconfinement) which were later observed by the NA49 experiment. The grand canonical ensemble was used to calculate entropy and strangeness production. This approximation is valid for reactions with mean multiplicities of particles carrying conserved charges being significantly larger than one. Recent results of NA61/SHINE on hadron production in inelastic p+p interactions suggest that the deconfinement may also take place in these reactions. However, in this case mean multiplicity of particles with non-zero strange charge is smaller than one. Thus for the modeling of p+p interactions the exact strangeness conservation has to be implemented in the SMES. This extension of the SMES is presented in the paper.

Low mass dilepton production in pp, p–Pb and Pb–Pb collisions with ALICE

Low mass vector meson ( ρ, ω, ϕ ) production provides key information on the hot and dense state of strongly interacting matter produced in high-energy heavy-ion collisions (called Quark-Gluon Plasma, QGP). Strangeness enhancement is one of the possible signatures of the Quark-Gluon Plasma formation and can be accessed through the measurement of ϕ meson production with respect to ρ and ω mesons. The production dynamics and hadronization process in relativistic heavy-ion collisions can be probed through the measurement of the ϕ nuclear modification factor.We present results on the low mass dimuon analysis in pp, p–Pb and Pb–Pb collisions. In pp collisions at √ s = 2.76 TeV the ϕ differential cross section as a function of the transverse momentum has been measured, serving as a baseline for Pb–Pb data.The ϕ yield and the nuclear modification factor R pPb at forward and backward rapidity have been measured for p–Pb collisions at √ s = 5.02 TeV. At forward rapidity, R pPb increases as a function of p T , saturating for p T > 3 GeV/ c at R pPb ~ 1. At backward rapidity, R pPb shows an increase as a function of the transverse momentum up to a factor of 1.6 for p T ~ 3-4 GeV/ c , followed by a decrease at higher p T .The ϕ yield and nuclear modification factor R AA have been measured for Pb–Pb collisions at √ s NN = 2.76 TeV in the intermediate p T region 2 p T c , as a function of the number of participating nucleons. Remarkable differences are observed in the comparison between the results at forward rapidity in the dimuon channel and the ones measured in the same p T range at midrapidity in the hadronic channel ϕ → KK .In the dielectron channel at midrapidity, the invariant mass distributions in the range 0 m ee c 2 are compared with the expected hadronic sources for pp collisions at √ s = 7 TeV, and for p–Pb collisions at √ s NN = 5.02 TeV. Latest results of the analysis of Pb–Pb collisions at √ s NN = 2.76 TeV are presented.

A Review onϕMeson Production in Heavy-Ion Collision

The main aim of the relativistic heavy-ion experiment is to create extremely hot and dense matter and study the QCD phase structure. With this motivation, experimental program started in the early 1990s at the Brookhaven Alternating Gradient Synchrotron (AGS) and the CERN Super Proton Synchrotron (SPS) followed by Relativistic Heavy Ion Collider (RHIC) at Brookhaven and recently at Large Hadron Collider (LHC) at CERN. These experiments allowed us to study the QCD matter from center-of-mass energies (sNN) 4.75 GeV to 2.76 TeV. Theϕmeson, due to its unique properties, is considered as a good probe to study the QCD matter created in relativistic collisions. In this paper we present a review on the measurements ofϕmeson production in heavy-ion experiments. Mainly, we discuss the energy dependence ofϕmeson invariant yield and the production mechanism, strangeness enhancement, parton energy loss, and partonic collectivity in nucleus-nucleus collisions. Effect of later stage hadronic rescattering on elliptic flow (v2) of proton is also discussed relative to corresponding effect onϕmesonv2.

Resonance Production with the LHCb Experiment

Studies of strange and charm resonance production in the forward region provide important input to the importance to the understanding of QCD models. The latest studies at LHCb of resonance production in both proton-proton and proton-lead collisions are presented, with particular emphasis on charmonium production including the production of Z (4430).

Strange and identified particle production with ALICE at the LHC

The ALICE experiment has measured the production of strange and identified charged particles in pp, p–Pb and Pb–Pb collisions at LHC energies. Light-flavour hadrons are identified in various momentum ranges by using specific energy loss, timeof-flight, Cherenkov radiation, as well as decay topology and invariant mass analysis for weakly-decaying strange particles.

Strange and identified particle production with ALICE at the LHC

The ALICE experiment has measured the production of strange and identified charged particles in pp, p–Pb and Pb–Pb collisions at LHC energies. Light-flavour hadrons are identified in various momentum ranges by using specific energy loss, timeof-flight, Cherenkov radiation, as well as decay topology and invariant mass analysis for weakly-decaying strange particles.In this contribution, the transverse momentum spectra at mid-rapidity and the corresponding yields measured in pp, p–Pb and Pb–Pb collisions for different multiplicity or centrality intervals are presented. The production of light-flavour hadrons in the three collision systems is compared and confronted with theoretical models.

S= −1 meson-baryon interaction in hot and dense nuclear matter: chiral symmetry, many-body and unitarization for a road to GSI/FAIR

The dynamics of strange pseudoscalar and vector mesons in hot and dense nuclear matter is studied within a chiral unitary framework in coupled channels. Our results set up the starting point for implementations in microscopic transport approaches of heavy-ion collisions, particularly at the conditions of the forthcoming experiments at GSI/FAIR and NICA-Dubna. In the K̄ N sector we focus on the calculation of (off-shell) transition rates for the most relevant binary reactions involved in strangeness production close to threshold energies, with special attention to the excitation of sub-threshold hyperon resonances and isospin effects (e.g. K̄ p vs K̄ n). We also give an overview of recent theoretical developments regarding the dynamics of strange vector mesons (K*, K̄* and ϕ) in the nuclear medium, in connection with experimental activity from heavy-ion collisions and nuclear production reactions. We emphasize the role of hadronic decay modes and the excitation of hyperon resonances as the driving mechanisms modifying the properties of vector mesons.

Evaluation of the MPD detector capabilities for the study of the strangeness production at the NICA collider

One of the main tasks of the NICA/MPD physics program is the study of the strangeness production in nuclear collisions. In this paper the MPD detector performance is presented for measurements of Ks0-mesons, \(\Lambda (\bar \Lambda )\)-hyperons and hypertritons in central Au + Au collisions at NICA energies.

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