Strange Quark Production Research Articles

Effect of color reconnection and rope formation on resonance production in p\u2013p collisions in Pythia 8

Resonance production in proton–proton collisions at sqrt{s} = 7 TeV and 13 TeV have been investigated using a Pythia 8 event generator within the framework of microscopic processes including color reconnection and rope hadronization. Specifically, the observable effects of different modes of color reconnections on the ratio of yields of mesonic and baryonic resonances with respect to their stable counterpart have been explored as a function of mean charged particle multiplicity. A suppression in the ratio is observed as a function of the mean number of charged particles for mesonic resonances. The phi /mathrm {K} and {phi /pi } ratios show an enhancement for high-multiplicity events due to enhanced production of strange quarks via the microscopic process of rope hadronization in the partonic phase. The mechanism of the hadronization of color ropes together with the quark–gluon plasma (QCD)-based color reconnection of partons predicted an enhancement in the ratio for baryonic resonances to non-resonance baryons having similar quark content. The yield ratios of resonances are found to be independent of the collision energy and strongly dependent on event activity.

Low-mass vector meson production at forward rapidity in p+p and d+Au collisions at $$\sqrt{s_{\rm NN}}$$ s NN = 200 GeV from a multiphase transport model

Low-mass vector meson (\(\rho , \omega \), and \(\phi \)) production at forward rapidity in p+p and d+Au collisions at \(\sqrt{s_{{\rm NN}}}\) = 200 GeV is studied within the framework of a multiphase transport model (AMPT). Detailed investigations, including the transverse momentum and the rapidity dependence of low-mass vector meson production in the AMPT model, show that the hadron interaction process is important for a quantitative description of the \(\rho \) and \(\omega \) data. But for the \(\phi \) meson, the strange quark production in the AMPT model with the string melting scenario describes the data reasonably well, while the default AMPT model under-predicts the data. The \({\rm N}(\phi )/{\rm N} (\rho + \omega )\) ratio from the AMPT model with the string melting scenario perfectly describes the data in p+p collisions. For the d+Au collisions, an increased trend of this ratio vs. transverse momentum and the number of participants are observed from the AMPT model. Our results indicate that a precise measurement of the \({\rm N}(\phi )/ {\rm N} (\rho + \omega )\) ratio in d+Au and Au+Au collisions will shed more light on the strangeness production and its dynamics in quark–gluon plasma.

Probing parton dynamics of QCD matter withΩandϕproduction

We present measurements of $\Omega$ and $\phi$ production at mid-rapidity from Au+Au collisions at nucleon-nucleon center-of-mass energies $\sqrt{s_{NN}}$ = 7.7, 11.5, 19.6, 27 and 39 GeV by the STAR experiment at the Relativistic Heavy Ion Collider (RHIC). Motivated by the coalescence formation mechanism for these strange hadrons, we study the ratios of $N(\Omega^{-}+\Omega^{+})/(2N(\phi))$. These ratios as a function of transverse momentum ($p_T$) fall on a consistent trend at high collision energies, but start to show deviations in peripheral collisions at $\sqrt{s_{NN}}$ = 19.6, 27 and 39 GeV, and in central collisions at 11.5 GeV in the intermediate $p_T$ region of 2.4-3.6 GeV/c. We further evaluate empirically the strange quark $p_T$ distributions at hadronization by studying the $\Omega/\phi$ ratios scaled by the number of constituent quarks. The NCQ-scaled $\Omega/\phi$ ratios show a suppression of strange quark production in central collisions at 11.5 GeV compared to $\sqrt{s_{NN}} >= 19.6$ GeV. The shapes of the presumably thermal strange quark distributions in 0-60% most central collisions at 7.7 GeV show significant deviations from those in 0-10% most central collisions at higher energies. These features suggest that there is likely a change of the underlying strange quark dynamics in the transition from quark-matter to hadronic matter at collision energies below 19.6 GeV.

Combustion of a hadronic star into a quark star: The turbulent and the diffusive regimes

We argue that the full conversion of a hadronic star into a quark or a hybrid star occurs within two different regimes separated by a critical value of the density of the hadronic phase $\overline{n_h}$. The first stage, occurring for $n_h>\overline{n_h}$, is characterized by turbulent combustion and lasts typically a few ms. During this short time-scale neutrino cooling is basically inactive and the star heats up thanks to the heat released in the conversion. In the second stage, occurring for $n_h<\overline{n_h}$, turbulence is not active anymore, and the conversion proceeds on a much longer time scale (of the order of tens of seconds), with a velocity regulated by the diffusion and the production of strange quarks. At the same time, neutrino cooling is also active. The interplay between the heating of the star due to the slow conversion of its outer layers (with densities smaller than $\overline{n_h}$) and the neutrino cooling of the forming quark star leads to a quasi-plateau in the neutrino luminosity which, if observed, would possibly represent a unique signature for the existence of quark matter inside compact stars. We will discuss the phenomenological implications of this scenario in particular in connection with the time structure of long gamma-ray-bursts.

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.

Production and energy loss of strange and heavy quarks

Data taken over the last several years have demonstrated that RHIC has created a hot, dense medium with partonic degrees of freedom. Identified particle spectra at high transverse momentum (pT) and heavy flavor that are thought to be well-calibrated probes thus serve as ideal tools to study the properties of the medium. We present pT distributions of particle ratios in p+p collisions from the STAR experiment to understand the particle production mechanisms. These measurements will also constrain fragmentation functions in hadron–hardon collisions. In heavy-ion collisions, we highlight (1) recent measurements of strange hadrons and heavy flavor decay electrons up to high pT to study jet interaction with the medium and explore partonic energy loss mechanisms, and (2) ϒ and high pT J/ψ measurements to study the effect of color screening and other possible production mechanisms.

Phenomenology of the three-flavor PNJL model and thermal strange quark production

We study the temperature dependence of the adjoint Polyakov loop and its implication for the momentum spectrum of gluons in the mean-field approximation. This allows us to calculate the contribution of the thermal (transverse) gluons to the thermodynamic pressure. As an application, we evaluate the rates for the strange quark pair-production processes and as functions of temperature including thermal effects on quark deconfinement and chiral symmetry breaking.

Strange prospects for LHC energies

Strange quark and hadron production will be studied at the large hadron collider (LHC) energies in order to explore the properties of both pp and heavy-ion collisions. The ALICE experiment will be specifically efficient in the strange sector with the identification of baryons and mesons over a wide range of transverse momentum. Dedicated measurements are proposed for investigating chemical equilibration and bulk properties. Strange particles can also help to probe kinematical regions where hard processes and pQCD dominate. We try to anticipate here several ALICE analyses to be performed as the first Pb–Pb and pp data will be available.

Perturbative dynamics of strangeness production at RHIC

Strange quark production in Au–Au collisions at RHIC is studied in the framework of the parton cascade model (PCM). The yields of (anti-) strange quarks for three production scenarios—primary–primary scattering full scattering and full production—are compared to a proton–proton baseline. Enhancement of strange quark yields in central Au–Au collisions compared to scaled p–p collisions increases with the number of secondary interactions. The centrality dependence of strangeness production for the three production scenarios is studied as well. For all production mechanisms, the strangeness yield increases with (Npart)4/3. The perturbative QCD regime described by the PCM is able to account for up to 50% of the observed strangeness at RHIC.

Strange quark production in an effective statistical model

Strangeness production in both high energy elementary and heavy ion collisions is described within the framework of an equilibrium statistical model with constituent quarks as fundamental degrees of freedom. The basic idea is that full local statistical equilibrium is achieved at the level of quark degrees of freedom. Besides the effect of different initial light flavour content and density, the smaller relative strangeness production in elementary with respect to heavy ion collisions is supposed to be related to the smaller system size and to colour confinement over small distances. Within an effective NJL model, fairly good agreement with the fitted Wroblewski factors λ s is found in high energy heavy ion and e +e − collisions, whilst a significant discrepancy shows up in pp collisions.

Strange quark production in a statistical effective model

An effective model with constituent quarks as fundamental degrees of freedom is used to predict the relative strangeness production pattern in both high energy elementary and heavy ion collisions. The basic picture is that of the statistical hadronization model, with hadronizing color-singlet clusters assumed to be at full chemical equilibrium at constituent quark level. Thus, by assuming that at least the ratio between strange and non-strange constituent quarks survives in the final hadrons, the apparent undersaturation of strange particle phase space observed in the data can be accounted for. In this framework, the enhancement of relative strangeness production in heavy ion collisions in comparison with elementary collisions is mainly owing to the excess of initial non-strange matter over antimatter and the so-called canonical suppression, namely the constraint of exact color and flavor conservation over small volumes.

Features of particle multiplicities and strangeness production in central heavy ion collisions between1.7Aand158A GeV/c

A systematic study is performed of fully integrated particle multiplicities in central Au-Au and Pb-Pb collisions at beam momenta of 1.7A GeV, 11.6A GeV (Au-Au) and 158$A$ GeV (Pb-Pb) by using a statistical-thermal model. The close similarity of the colliding systems makes it possible to study heavy ion collisions under definite initial conditions over a range of centre-of-mass energies covering more than one order of magnitude. In order to further study the behaviour of strangeness production, an updated study of Si-Au collisions at 14.6A GeV is also presented. The data analysis has been performed with two completely independent numerical algorithms giving closely consistent results. We conclude that a thermal model description of particle multiplicities, with additional strangeness suppression, is possible for each energy. The degree of chemical equilibrium of strange particles and the relative production of strange quarks with respect to u and d quarks are higher than in e+e-, pp and ppbar collisions at comparable and even at lower energies. The behaviour of strangeness production as a function of centre-of-mass energy and colliding system is presented and discussed. The average energy per hadron in the comoving frame is close to 1 GeV per hadron despite the fact that the energy increases more than 10-fold.

CHEMICAL EVOLUTION OF STRONGLY MAGNETIZED QUARK CORE IN A NEWBORN NEUTRON STAR

The chemical evolution of nascent quark matter core in a newborn compact neutron star is studied in presence of a strong magnetic field. The effective rate of strange quark production in degenerate quark matter core in presence of strong magnetic fields is obtained. The investigations show that in presence of strong magnetic field the quark matter core becomes energetically unstable and hence a first/higher order deconfinement transition to quark matter at the centre of a compact neutron star under such circumstances is absolutely impossible. The critical strength of magnetic field at the central core to make the system energetically unstable with respect to dense nuclear matter is found to be ~4.4 × 1013 G. This is the typical strength at which the Landau levels for electrons are populated. The other kind of phase transformations at such high density and ultra strong magnetic field environment are discussed.

Strangeness counting in high energy collisions

The estimates of overall strange quark production in high energy , pp and pp collisions by using the statistical-thermal model of hadronization are presented and compared with previous works. The parametrization of strangeness suppression within the model is discussed. Interesting regularities emerge in the strange/non-strange produced quark ratio which turns out to be fairly constant in elementary collisions while it is twice as large in SPS heavy ion collision.

Antihyperon-hyperon production in p¯p annihilations near the reaction thresholds

The PS 185 experiment at LEAR/CERN studies strangeness production in antiproton-proton collisions in flight. Exclusive final states containing pairs of antihyperons and hyperons have been analysed. The data have been used to investigate strange quark production dynamics. New data at the highest energies available at LEAR extend the existing data set for the Λ¯Λ channel. Preliminary data from a new threshold scan are available. For the Σ¯ 0 Λ+cc channel first spin correlation data have been extracted. First preliminary differential cross section data from the Σ¯ − Σ − channel are also presented.

Strangeness production in neutron stars

Production of strange quarks in neutron stars is investigated in this work. Three cases, one in which the energy and neutrinos produced in the strangeness production reactions are retained in the reaction region, second in which the neutrinos are allowed to escape the reaction region but the energy is retained and the third in which both the energy and neutrinos escape the reaction region are considered. It is shown that the nonleptonic weak process dominates strange quark production while semileptonic weak processes, which produce neutrinos, lead to the cooling if the neutrinos escape the reaction region. It is found that the time required for the saturation of the strangeness fraction is between $10^{-7}$ and $10^{-5}$ sec, with the shorter time corresponding to the first two cases. About 0.2 neutrinos/baryon are emitted during the process in the first two cases where as the neutrino emission is somewhat suppressed in the last case. The average energy of the neutrinos produced in all the three cases is found to be several hundred $MeV$. We also find that a large amount of energy is released during the strangeness production in the first two cases and this leads to the heating of the reaction region. Implications of the neutrino production are investigated.

Production of Strange Quarks from Nuclear Matter and Their Polarization : Polarized &Lambda; Hyperons Produced in &pi;-Nucleus Reactions

Production of Strange Quarks from Nuclear Matter and Their Polarization : Polarized &Lambda; Hyperons Produced in &pi;-Nucleus Reactions

Fireball production in a quark-gluon plasma and the equilibrium of strange quarks

We study the quark-gluon plasma produced in nucleus-nucleus collisions where the laboratory kinetic energy goes from 4 to 25 GeV/ nucleon. The strange quark production is analyzed in detail and we look at the possibility for the plasma to lose energy by fireball production. Such fireballs are created inside the plasma via the dominent two-gluon fusion mechanism. Our results disagree with those of Biro and Zimanyi concerning the equilibrium of the strange quark population. A prediction is made for the 15 GeV/nucleon BNL sulfur beam and for uranium-uranium collisions at 25 GeV/nucleon. In the most energetic case of uranium we obtain a saturation ratio of no more than 25%. On the other hand, a low amount of energy carried by the fireballs leads to an important increase of the ratio $${{N_s } \mathord{\left/ {\vphantom {{N_s } {N_{\bar q} }}} \right. \kern-\nulldelimiterspace} {N_{\bar q} }}$$ . Using reasonable values for the parameters, we find that this ratio may reach a value of 3.5 in the most favorable case of uranium.

Strangeness production in the quark gluon plasma

It is shown that perturbative QCD predicts abundant strange quark production in the plasma created in high energy nuclear collisions. Considering further the strange particle production in the hadronic gas phase, I show that the strangeness abundance in the plasma is 10–50 times higher as compared with the gas phase in similar thermodynamic conditions. Possible experiments leading to the identification of the plasma phase are described.

Quark model for multiparticle and inclusive reactions

The relative multiplicity of different hadrons produced in high-energy collisions is found in the framework of the quark model. Appart from the usual hypothesis about the quark structure of hadrons, two extra assumptions are made. Firstly, produced particles are supposed to be mainly the members of the meson 36-plet and baryon (antibaryon) 56-plet. Secondly, production of strange quarks is assumed to be suppressed relative to non-strange quarks roughly by a factor of three, as taken from experiment. In the small- x region the agreement with experimental data is satisfactory. In the fragmentation region it is necessary to take into account the kinematics of the resonant state's decay. The influence of such decay on the x and p T 2 distributions of hadrons is discussed.