Strange Particles Research Articles

Study of Σ(1385) and Ξ(1321) hyperon and antihyperon production in deep inelastic muon scattering

Large samples of \Lambda, \Sigma(1385) and \Xi(1321) hyperons produced in deep-inelastic muon scattering off a ^6LiD target were collected with the COMPASS experimental setup at CERN. The relative yields of \Sigma(1385)^+, \Sigma(1385)^-, \bar{\Sigma}(1385)^-, \bar{\Sigma}(1385)^+, \Xi(1321)^-, and \bar{\Xi}(1321)^+ hyperons decaying into \Lambda(\bar{\Lambda})\pi were measured. The heavy hyperon to \Lambda and heavy antihyperon to \bar{\Lambda} yield ratios were found to be in the range 3.8% to 5.6% with a relative uncertainty of about 10%. They were used to tune the parameters relevant for strange particle production of the LEPTO Monte Carlo generator.

Measurement of neutral strange particle production in the underlying event in proton-proton collisions ats=7 TeV

Measurements are presented of the production of primary KS0 and Λ particles in proton-proton collisions at s=7 TeV in the region transverse to the leading charged-particle jet in each event. The average multiplicity and average scalar transverse momentum sum of KS0 and Λ particles measured at pseudorapidities |η|<2 rise with increasing charged-particle jet pT in the range 1–10 GeV/c and saturate in the region 10–50 GeV/c. The rise and saturation of the strange-particle yields and transverse momentum sums in the underlying event are similar to those observed for inclusive charged particles, which confirms the impact-parameter picture of multiple parton interactions. The results are compared to recent tunes of the pythia Monte Carlo event generator. The pythia simulations underestimate the data by 15%–30% for KS0 mesons and by about 50% for Λ baryons, a deficit similar to that observed for the inclusive strange-particle production in non-single-diffractive proton-proton collisions. The constant strange- to charged-particle activity ratios with respect to the leading jet pT and similar trends for mesons and baryons indicate that the multiparton-interaction dynamics is decoupled from parton hadronization, which occurs at a later stage.Received 26 May 2013DOI:https://doi.org/10.1103/PhysRevD.88.052001This article is available under the terms of the Creative Commons Attribution 3.0 License. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.© 2013 CERN, for the CMS Collaboration

Strangeness production in ALICE

The ALICE experiment at the LHC has measured the production of strange and multi-strange hadrons both in Pb–Pb and pp collisions at unprecedented beam energies. Transverse momentum spectra at mid-rapidity for K0S mesons, Λ, and Ω− baryons and their anti-particles in Pb–Pb collisions at TeV are presented in different centrality intervals. Particles are reconstructed via their weak decay topologies into charged particles only over a wide momentum range, exploiting the tracking and particle identification capabilities of the ALICE detector. The corresponding production yields are compared with those observed in pp collisions and lower energy heavy-ion reactions. In particular, results on baryon-to-meson ratio, strangeness enhancements, elliptic flow and nuclear modification factors are discussed. The comparison of strange particle spectra in pp collisions at TeV with PYTHIA Perugia-2011 predictions is also presented.

Topological superconductivity without proximity effect

Majorana fermions, strange particles that are their own antiparticles, were predicted in 1937 and have been sought after ever since. In condensed matter they are predicted to exist as vortex core or edge excitations in certain exotic superconductors. These are topological superconductors whose order parameter phase winds nontrivially in momentum space. In recent years, a new and promising route for realizing topological superconductors has opened due to advances in the field of topological insulators. Current proposals are based on semiconductor heterostructures, where spin-orbit-coupled bands are split by a band gap or Zeeman field and superconductivity is induced by proximity to a conventional superconductor. Topological superconductivity is obtained in the interface layer. The proposed heterostructures typically include two or three layers of different materials. In the current work we propose a device based on materials with inherent spin-orbit coupling and an intrinsic tendency for superconductivity, eliminating the need for a separate superconducting layer. We study a lattice model that includes spin-orbit coupling as well as on-site and nearest-neighbor interaction. Within this model we show that topological superconductivity is possible in certain regions of parameter space. These regions of nontrivial topology can be understood as a nodeless superconductor with $d$-wave symmetry which, due to the spin-orbit coupling, acquires an extra phase twist of $2\ensuremath{\pi}$.

Dynamical Interpretation of Spurions

The concept of spurions was introduced originally as a formal mathematical tool to express the selection rule \Al\/2 in the non-leptonic decay of strange particles. It is shown in the present article that spurions are of a deeper physical significance in that they can be used not only to express but also to derive selection rules in weak interactions. DYNAMICAL INTERPRETATION OF SPURIONS

Compact stars and the symmetry energy

The effect of the symmetry energy on some properties of compact stars which contain strange degrees of freedom is discussed. Both the onset of hyperons or kaon condensation will be considered. The hyperon-meson couplings are chosen according to experimental values of the hyperon nuclear matter potentials and possible uncertainties are considered. It is shown that a softer symmetry energy affects the onset of strangeness, namely neutral (negatively charged) strange particles set on at larger (smaller) densities, and gives rise to a smaller strangeness fraction as a function of density. A softer symmetry energy will possibily give rise to maximum mass configurations with larger masses. Hyperon-meson couplings have a strong effect on the mass of the star. It is shown that, for stars with masses above 1 M⊙, the radius of the star varies linearly with the symmetry energy slope L.

Strange particle production in proton-carbon interactions at 31 GeV/c

Spectra of positively charged kaons in p+C interactions at 31 GeV/c have been measured with the NA61/SHINE spectrometer at CERN SPS. The analysis is performed on the dataset collected during the 2007 pilot run (about 678×103 events). The target is a 2 cm long graphite specimen (4% of a nuclear interaction length λI). Charged pion spectra have been already measured with the same dataset [1]. Pion and kaon differential production cross sections are required to improve predictions of the neutrino flux for the T2K long baseline neutrino oscillation experiment in Japan. The knowledge of kaon production is especially important for the precise prediction of the intrinsic electron neutrino component of the T2K beam. The results are presented as a function of laboratory momentum in 2 intervals of the laboratory polar angle covering the range from 20 up to 240 mrad. Kaon spectra as well as K+/π+ ratios are compared with predictions of several hadron production models. In addition, first results from the analysis of the high statistics 2009 data taking are shown.

Strange particle measurements at the CERN SPS – NA49 and NA61/SHINE experiments

Abstract Strangeness production in heavy-ion collisions has always been an important observable for probing the state of matter created in these collisions. In particular, relative strangeness production, its event-by-event fluctuations as well as their dependence on the collision energy and centrality are sensitive probes of the deconfinement phase transition. This contribution presents selected NA49 and NA61/SHINE results on strangeness production in central Pb + Pb collisions and p + p interactions in the SPS energy range. Special attention is given to data on particle ratios and ratio fluctuations as well as K ⁎ , K ¯ ⁎ resonance production.

In-medium effects on strangeness production

We discuss the strangeness production close to threshold in heavy-ion collisions based on two independent microscopic transport approaches – HSD and IQMD – employing different in-medium scenarios for the modification of particle properties (strange mesons and hyperons) in the dense and hot medium following either from the chiral models or from a coupled-channel G -matrix approach using a meson-exchange model for strange mesons. The comparison of available kaon, antikaon and Λ data with the HSD and IQMD models shows a good agreement for the large majority of observables when incorporating the in-medium effects. The investigation of the reactions with help of transport models reveals the complicated multiple interactions of the strange particles with hadronic matter which shows that strangeness production in heavy-ion collisions is very different from that in elementary interactions. We discuss how a variety of strange particle observables can be used to study the different facets of this interaction (production, rescattering and potential interaction) which finally merge into a comprehensive understanding of these reactions.

An algebraic approach to QCD and superconduction

The SU3 spin connections in an Elliptic Space are found to provide the two vortices at an angle of ω = 120 degrees shown in Fig.3.Then by relating the vertices of the 24-cell,labeled by 0, ±1 ,ω , ω 2 to quarks and leptons,we can show that they all occupy elliptic spaces. In particular Fig.3 could illustrate a Cooper pair of electrons,if cold enough.Otherwise a single electron, which can inhabit either vortex core, may act as a link in a superconducting chain on a nanowire at a finite temperature.Furthermore we will find that the three quarks in a proton,neutron or strange particle are distinguished by a rotation through ω .T hus if we consider the 6 paths of fig.3 to be two sets of gluons labeled by r,b,g and r, b, r and add the possible rotations between quarks we can incorporate gluon bindings such as rb, rg and so on, which are a basis for the SU3 symmetry underlining QCD.

Nucleon resonance production in K+N interactions

In this work, we discuss the possibility of studying nucleon resonances in the $K^+N$ interactions. Based on our model calculations, it is found that the hyperon exchange plays an important role for the excitation of nucleon resonances in the $K^+N$ interactions. Therefore, the studies on nucleon resonance production in the $K^+N$ interactions can offer us valuable information about the couplings of nucleon resonances with strange particles. By selecting suitable decay channels of nucleon resonances, some reactions are also suitable to look for missing resonances.

A trigger based on an active target for the MIS ITEP experimental setup

The use of a silicon photomultiplier (SiPM) has made it possible to produce a compact target composed of 16 active elements capable of measuring ionization losses in each element. The accuracy of a single ionization measurement is sufficient to allow discrimination between single- and three-track signals in 90% of events. A special ΛЭ-80 processor has been developed using the programmable decision lookup table method for trigger signal generation, which is implemented in Altera programmable logic devices. The time it takes for the special processor to produce a trigger signal is 80 ns or less. The possibility of separating reactions with neutral strange particles has been demonstrated using vast experimental statistics.

Elliptic flow of charged pions, protons and strange particles emitted in Pb+Au collisions at top SPS energy

Differential elliptic flow spectra v 2 ( p T ) of π − , K S 0 , p , Λ have been measured at s NN = 17.3 GeV around midrapidity by the CERN-CERES/NA45 experiment in mid-central Pb + Au collisions (10% of σ geo ). The p T range extends from about 0.1 GeV/ c (0.55 GeV/ c for Λ ) to more than 2 GeV/ c . Protons below 0.4 GeV/ c are directly identified by d E / d x . At higher p T , proton elliptic flow is derived as a constituent, besides π + and K + , of the elliptic flow of positive pion candidates. This retrieval requires additional inputs: (i) of the particle composition, and (ii) of v 2 ( p T ) of positive pions. For (i), particle ratios obtained by NA49 are adapted to CERES conditions; for (ii), the measured v 2 ( p T ) of negative pions is substituted, assuming π + and π − elliptic flow magnitudes to be sufficiently close. The v 2 ( p T ) spectra are compared to ideal-hydrodynamics calculations. In synopsis of the series π − – K S 0 – p – Λ , flow magnitudes are seen to fall with decreasing p T progressively even below hydro calculations with early kinetic freeze-out ( T f = 160 MeV ) leaving not much time for hadronic evolution. The proton v 2 ( p T ) data show a downward swing towards low p T with excursions into negative v 2 values. The pion-flow isospin asymmetry observed recently by STAR at RHIC, invalidating in principle our working assumption, is found in its impact on proton flow bracketed from above by the direct proton flow data, and not to alter any of our conclusions. Results are discussed in perspective of recent viscous hydrodynamics studies which focus on late hadronic stages.

Event-by-event fluctuations of particle ratios in heavy-ion collisions

We have studied the event-by-event dynamical fluctuations of some particle yield ratios at various incident energies. We have assumed that the particle production in the final state is due to chemical equilibrium processes. We have compared the results from the hadron resonance gas (HRG) model with the available experimental data. At energies up to SPS, the HRG model can very well reproduce the experimentally measured fluctuations. To reproduce RHIC results, the quark phase space occupancy parameter is allowed to vary. Furthermore, we have made predictions for the dynamical fluctuations of strange and non-strange particle ratios. We have found that the overall energy-dependence is non-monotonic. We have also found that the fluctuations strongly depend on the various species of particle ratios.

Production of hypernuclei in peripheral collisions of relativistic ions

Abstract Formation of hypernuclei in peripheral collisions of relativistic light and heavy ions is studied theoretically within the transport and statistical approaches. New mechanisms for the formation of strange nuclear systems via capture of hyperons by slightly excited spectator matter and their subsequent disintegration are investigated. These processes lead to production of specific and exotic hypernuclei, which may not be accessible in other reactions. Similar mechanisms processing via absorption of strange particles by nuclei can take place in reactions initiated by electrons, antiprotons and other hadrons. It is demonstrated that our approach is consistent with experimental data.

Transverse momentum distributions of strange hadrons produced in nucleus–nucleus collisions at and 200 GeV

The transverse momentum distributions of strange particles produced in high-energy collisions are analyzed by the thermalized cylinder model. We present a detailed comparison with the experimental data of Cu+Cu and Au+Au collisions at = 62.4 and 200 GeV. It is found that the calculated results are in agreement with the experimental data. The excitation degree of an emission source on the central axis of the cylinder increases obviously with increasing collision centrality and incident energy. There is no obvious change in the excitation degree of the emission source in the side-surface of the cylinder.

Strange and multi-strange particle production at the LHC energies with ALICE

Strange quark and particle production is studied at the LHC with unprecedented high beam energies in both heavy-ion and proton-proton collisions: on the one hand, strangeness is used for investigating chemical equilibration and bulk properties; on the other hand, strange particles contribute to probe different kinematical domains, from the one where collective phenomena are at play up to the region dominated by pQCD-calculable processes. We highlight the suitability of the ALICE experiment for this topic, presenting our latest measurements and comparing them to models.

Characteristics of Strange Hadron Production in Some High Energy Collisions and the Role of Power Laws

Studies on `strange' particle production have always occupied a very important space in the domain of Particle Physics. This was and is so, just because of some conjectures about specially abundant or excess production of `strange' particles, at certain stages and under certain conditions arising out of what goes by the name of `Standard' model in Particle Physics. With the help of Hagedornian power laws we have attempted to understand and interpret here the nature of the $p_T$-spectra for the strange particle production in a few high energy nuclear collisions, some interesting ratio-behaviours and the characteristics of the nuclear modification factors that are measured in laboratory experiments. After obtaining and analysing the final results we do not confront any peculiarities or oddities or extraneous excesses in the properties of the relevant observables with no left-over problems or puzzles. The model(s) used by us work(s) quite well for explaining the measured data.

Nonextensive statistical effects in the quark-gluon plasma formation at relativistic heavy-ion collisions energies

AbstractWe investigate the relativistic equation of state of hadronic matter and quark-gluon plasma at finite temperature and baryon density in the framework of the non-extensive statistical mechanics, characterized by power-law quantum distributions. We impose the Gibbs conditions on the global conservation of baryon number, electric charge and strangeness number. For the hadronic phase, we study an extended relativistic mean-field theoretical model with the inclusion of strange particles (hyperons and mesons). For the quark sector, we employ an extended MIT-Bag model. In this context we focus on the relevance of non-extensive effects in the presence of strange matter.

Strange particle production in relativistic collisions of heavy ions

This review examines data on strange particle production in Pb + Pb collisions obtained in heavy ion experiments at CERN SPS. The yields of K, Λ, Ξ and Ω are considered, as well as their rapidity and transverse mass distributions, depending on the centrality of Pb + Pb collisions at SPS energies. Experimental results are compared with predictions of the statistical nuclear fireball and microscopic parton -string models. We discuss in detail the experimentally observed effect of strangeness enhancement in nucleus-nucleus collisions as compared to nucleon-nuclear interactions and its interpretation within the framework of various theoretical models. Also, we analyze the behavior of hyperon yields and nuclear modification factors in passing from SPS to RHIC energies.