Properties of Strange Matter in a Model with Effective lagrangian

The strange hadronic mater with nucleons,Λ-hyperons and Ξ-hyperons is studied by using an effective nuclear model in a mean-field approximation.The density and strangeness fraction dependence of the effective baryon masses as well as the saturation properties and stabilities of the strange hadronic matter are discussed.     

Hot Strange Hadronic Matter in an Effective Model

An effective model used to describe the strange hadronic matter with nucleons, A-hyperons, and [I]-hyperons is extended to finite temperature. The extended model is used to study the density, temperature, and strangeness fraction dependence of the effective masses of baryons in the matter. The thermodynamical quantities, such as free energy and pressure, as well as the equation of state of the matter, are given.     

Hot Strange Hadronic Matter in an Effective Model

An effective model used to describe the strange hadronic matter with nucleons, Λ-hyperons, and Ξ-hyperonsis extended to finite temperature. The extended model is used to study the density, temperature, and strangeness fractiondependence of the effective masses of baryons in the matter. The thermodynamical quantities, such as free energy andpressure, as well as the equation of state of the matter, are given.     

MULTI-LAMBDA MATTER IN A CHIRAL HADRONIC MODEL

Multi-lambda matter is investigated in the framework of a chiral hadronic model. It is shown that multi-lambda matter consisting of {N,Λ} is a metastable state as the strangeness per baryon and the density of hadronic matter are varied. The effective lambda mass decreases as the baryon density increases, and remains larger than that of the nucleon.     

Hyperon coupling dependence of hadron matter properties in relativistic mean field model

The properties of hadronic matter at β equilibrium in a wide range of densities are described by appropriate equations of state in the framework of the relativistic mean field model. Strange meson fields, namely the scalar meson field σ＊（975） and the vector meson field φ（1020）, are included in the present work. We discuss and compare the results of the equation of state, nucleon effective mass, and strangeness fraction obtained by adopting the TM1, TMA, and GL parameter sets for nuclear sector and three different choices for the hypcron couplings. We find that the parameter set TM1 favours the onset of hyperons most, while at high densities the GL parameter set leads to the most hyperon-rich matter. For a certain parameter set （e.g. TM1）, the most hyperon-rich matter is obtained for the hyperon potential model. The influence of the hyperon couplings on the effective mass of nucleon, is much weaker than that on the nucleon parameter set. The nonstrange mesons dominate essentially the global properties of dense hyperon matter. The hyperon potential model predicts the lowest value of the neutron star maximum mass of about 1.45 Msun to be 0.4--0.5 Msun lower than the prediction by using the other choices for hyperon couplings.[第一段]     

奇异强子与核子的相互作用

包含s夸克的强子称为奇异强子,它与核子相互作用的研究近年来有了长足发展 .在指出这种研究的重要意义后,从实验和理论两方面介绍奇异强子 (主要是K介子和超子 )与核子相互作用的研究现状及方法等 ,包括运动学和动力学机制、介子交换模型和夸克模型解释诸方面的问题. We try to highlight some of the key issues regarding the interactions between strange hadron and nucleon, which relate to the kinematics and dynamics mechanism, meson exchange model and quark model. Starting from a brief introduction on the main research goals, we focus on the status of experimental and theoretical investigations of kaon nucleon and hyperon nucleon interactions, which may be considered to be a necessary basis for the studies of nuclear physics with strangeness.     

Deconfinement Phase Transition Including Perturbative QCD Corrections in （Proto）neutron Star Matter

Deconlinement phase transition and neutrino trapping in （proto）neutron star matter are investigated in a chiral hadronic model （also referred to as the FST model） for the hadronic phase （HP） and in the color-flavor-locked （CFL） quark model for the deconlined quark phase. We include a perturbative QCD correction parameter αs in the CFL quark matter equation of states. It is shown that the CFL quark core with K^0 condensation forms in neutron star matter with the large value of αs. If the small value of αs is taken, hyperons suppress the CFL quark phase and the liP is dominant in the high-density region of （proto）neutron star matter. Neutrino trapping makes the fraction of the CFL quark matter decrease compared with those without neutrino trapping. Moreover, increasing the QCD correction parameter as or decreasing the bag constant B and the strange quark mass ms can make the fraction of the CFL quark matter increase, simultaneously, the fraction of neutrino in protoneutron star matter increases, too. The maximum masses and the corresponding radii of （proto）neutron stars are not sensitive to the QCD correction parameter αs.     

强和弱Y-Y相互作用下的奇异强子物质

把修正的夸克-介子耦合模型推广到包含奇异性的情形， 并用来研究奇异强子物质的状态方程. 从最新的6ΛΛHe双超核的实验导出的弱Λ Λ相互作用和过去采用的强Λ Λ相互作用同时被用于计算. 比较发现， 具有强Λ-Λ相互作用的系统束缚得比正常核物质要紧， 而具有弱Λ Λ相互作用的系统则比正常核物质束缚得要松得多. 无论强还是弱相互作用情况， 为了合适地描述修正的夸克 介子耦合模型中超子-超子（Y Y）相互作用， 必须引进σ*和介子. A modified quark meson coupling (MQMC) model is extended to include Λ hyperons and Ξ hyperons. The extended model is then used to study the equation of state (EOS) for strange hadronic matter. A weak Λ Λ interaction deduced from recent observation of 6ΛΛHe double hypernucleus is adopted in the calculation. The resultant EOS is compared with that deduced from a strong Λ Λ interaction. It is found that while the system with the strong ΛΛ interaction is more deeply bound than ordinary nuclear matter due to the opening of new degrees of freedom， the system with the weak Λ Λ interaction is rather loosely bound compared to the later. It is necessary to introduce the strange mesons σ*and in the MQMC model to describe properly the interaction between the hyperons in either strong or weak ΛΛ interaction case.     

兰州冷却储存环上可开展的强子物理研究

介绍了当前强子物理的研究现状和兰州冷却储存环的能量特点,以及国内强子物理专家的分析和建议。在兰州冷却储存环上,可利用中能轻离子束核反应产生强子激发态研究强子内部夸克态的结构和性质、强子性质随核环境的变化和手征对称破缺与部分恢复。尤其是通过兰州冷却储存环上限能区附近的P＋P反应,研究奇异夸克的不对称性和形状因子,寻找超子激发态和pentaquark的实验证据,发现双重子态的实验事例。 According to both the development on badrons physics and the aspect of Lanzhou cooling storage ring （CSR） and based on the analysis and propositions given by experts in China, we propose some hadrons physics program at CSR. The hadron spectroscopy produced in light nucleus collisions at CSR used to probe the quark and gluon structure of hadrons, to study the modification of the hadron properties in nuclear matter and to investigate the spontaneous breaking of the chiral symmetry and its partial restoration. Especially, the proton-proton collisions at beam energies per proton below 2.8 GeV at CSR should be used to measure the strangeness asymmetry and strange form lector, to probe the existence of hyperon and pentaquarks and to find the evidence for the existence of dibaryon.     

Properties of color-flavor locked strange quark matter and strange stars in a new quark mass scaling

Considering the effect of one-gluon-exchange interaction between quarks,the color-flavor locked strange quark matter and strange stars are investigated in a new quark mass density-dependent model.It is found that the color-flavor locked strange quark matter can be more stable if the one-gluon-exchange effect is included.The lower density behavior of the sound velocity in this model is different from the previous results.Moreover,the new equation of state leads to a heavier acceptable maximum mass,supporting the recent observation of a compact star mass as large as about 2 times the solar mass.     

Kaon and antikaon optical potentials in isospin asymmetric hyperonic matter

The medium modifications of the energies of kaons and antikaons in isospin asymmetric hyperonic matter are investigated using a chiral SU(3) model. The isospin-dependent medium effects are important for asymmetric heavy-ion collision experiments, as well as relevant for the neutron star phenomenology as the bulk matter in the interior of the neutron star is highly isospin asymmetric. The effects of hyperons on the medium modifications of the kaons and antikaons in the strange hadronic matter are investigated in the present work and are seen to be appreciable for hadronic matter with large strangeness fractions. The study of the K -mesons in the asymmetric strange hadronic matter can be especially relevant for the compressed strange baryonic matter which can result from asymmetric heavy-ion collision experiments in the future accelerator facility FAIR at GSI.     

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

We 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.     

Multiplicity distribution of strange particles in heavy ion collisions

We study the multiplicity distribution of strange particles in a hadronic gas constrained by exact strangeness conservation. The multiplicity distribution obtained is narrower than both the Poisson and negative binomial distributions. Correlations among strange particles are also discussed. The results presented might be useful in determining the thermodynamic parameters (volume, temperature and baryon density) of a hadronic gas possibly formed in relativistic nuclear collisions.     

Strange hadrons – strangeness in strongly interacting particles Strangeness production with KAOS at MAMI

In 2007 the Mainz Microtron MAMI has been upgraded to 1.5 GeV electron beam energy, crossing the energy threshold for open strangeness production. The strangeness quantum number, as carried by the strange quark, provides valuable information on the contribution of individual quark flavours to hadronic processes. Theoretically, the strange quark with its rest energy of order 150 MeV is particularly interesting because it can neither be treated as a massless nor as a heavy quark. Experimentally, an instrument of central importance for the charged kaon electro-production off the proton or light nuclei at MAMI is the magnetic spectrometer Kaos that was installed recently and is now routinely operated by the A1 collaboration.     

Strange hadronic matter in a modified quark-meson coupling model

Strange hadronic matter with nucleons, Λ-hyperons and Ξ-hyperons is studied by using a modified quark-meson coupling (MQMC) model in a mean-field approximation. The density dependence of the effective baryon masses as well as the saturation properties and stabilities of the strange hadronic matter are discussed.     

Quark-hadron phase transition and strangeness conservation constraints

The implications of the strangeness conservation in a hadronic resonance gas (HRG) on the expected phase transition to the quark gluon plasma (QGP) are investigated. It is assumed that under favourable conditions a first order hadron-quark matter phase transition may occur in the hot hadronic matter such as those produced in the ultra-relativistic heavy-ion collisions at CERN and BNL. It is however shown that the criteria of strict strangeness conservation in the HRG may not permit the occurrence of a strict first order equilibrium quark-hadron phase transition unlike a previous study. This emerges as a consequence of the application of a realistic equation of state (EOS) for the HRG and QGP phases, which account for the finite-size effect arising from the short range hard-core hadronic repulsion in the HRG phase and the perturbative QCD interactions in the QGP phase. For a first order hadron-quark matter phase transition to occur one will therefore require large fluctuations in the critical thermal parameters, which might arise due to superheating, supercooling or other nonequlibrium effects. We also discuss a scenario proposed earlier, leading to a possible strangeness separation process during hadronization. Received: 25 August 1997 / Revised version: 25 March 1998 / Published online: 26 August 1998