Rapidity dependence of global polarization in heavy ion collisions

We use a geometric model for hadron polarization in heavy ion collisions with an emphasis on the rapidity dependence.The model is based on the model of Brodsky,Gunion,and Kuhn,as well as the Bjorken scaling model.We make predictions regarding the rapidity dependence of global Λ polarization in the collision energy range of 7.7-200 GeV by assuming the rapidity dependence of two parameters,κ and <ρτ>. The predictions can be tested by future beam-energy-scan experiments at the Relativistic Heavy Ion Collider of Brookhaven National Lab.     

Strangeness by Thermal Model Simulation at RHIC

The local temperature effect on strangeness enhancement in relativistic heavy ion collisions is discussed in the framework of the thermal model in which the K^＋ /h^＋ ratio becomes smaller with increasing freeze-out temperature. Considering that most strangeness particles of final-state particles are from the kaon meson, the temperature effect may play a role in strangeness production in hot dense matter where a slightly different temperature distribution in different areas could be produced by jet energy loss. This phenomenon is predicted by thermal model calculation at RHIC energy. The /Ф ratio in central Au＋Au collisions at 200GeV from the thermal model depends on the freeze-out temperature obviously when γs is different. It should be one of the reasons why strangeness enhancements of and Ф are different though they include two strange quarks. These results indicate that thermodynamics is an important factor for strangeness production and the strangeness enhancement phenomenon.     

Rayleigh-like distribution of particle transverse momenta in collisions at high energies

The transverse momentum distributions of final-state particles produced in collisions at high en-ergies are studied by using a two-component Rayleigh-like distribution.This representation is based on Liu＇s multisource ideal gas model which describes protons and fragments in high energy nucleus-nucleus collisions.The calculated results are in good agreement with the experimental data of Au-Au,Cu-Cu,d-Au,and pp collisions at the relativistic heavy ion collider energies.The experimental particle momentum distributions of p-Be collisions at 6.4,12.3,and 17.5 GeV/c,as well as Au-Au collisions at 1.5 AGeV are well described by a model based on a single Rayleigh-like distribution of particle transverse momenta.     

Transverse Flow of Kaons in Heavy—Ion Collisions

The transverse flow of positively charged kaons from heavy-ion collisions at intermediate energy is investigated within the framework of the quantum molecular dynamics model.The calculated results whow that the experimental data are only consistent with those including the kaon mean-field potential from the chiral Lagrangian.This indicates that the transverse flow pattern of kaons is a useful probe of the kaon potential in a nuclear medium.     

Interferometry Signatures for QCD First-Order Phase Transition in High Energy Heavy Ion Collisions

Using the technique of quantum transport of the interfering pair we examine the Hanbury-Brown-Twiss （HBT） interferometry signatures for the particle-emitting sources of pions and kaons produced in heavy ion collisions at 10-30 AGeV. The evolution of the sources is described by relativistic hydrodynamics with the first-order phase transition from quark-gluon plasma （QGP） to hadronic matter. We use quantum probability amplitudes in a path-integral formalism to calculate the two-particle correlation functions, where the effects of particle decay and multiple scattering are taken into consideration. Our model-calculated results indicate that both the HBT radii of pions and kaons increase with the system initial energy density. The HBT lifetimes of the pion and kaon sources increase significantly when the initial energy density is tuned to the phase boundary between the QGP and mixed phase. This increase of HBT lifetimes will likely appear in heavy ion collisions with an incident energy between 10-30 AGeV.     

Anisotropic emission of charged mesons and structure characteristic of emission source in heavy ion collisions at 1-2A GeV

Angular distributions of pious and kaons produced in heavy ion collisions at the low-energy end of high energies （1-2 A GeV） have been investigated by using a multisource ideal gas model. The model covers the expansions and movements of the emission sources, and it is related to the collective flows. By using the analytic expression and the Monte Carlo method, the azimuthal and polar angle distributions of mesons are calculated by the model and compared with the experimental data of the KaoS Collaboration.     

Surface Emission of Quark Gluon Plasma at RHIC and LHC

Within the framework of a factorization model, we study the behaviour of nuclear modification factor in Au Au collisions at RHIC and Pb-Pb collisions at LHC. We find that the nuclear modification factor is inversely proportional to the radius of the quark-gluon plasma and is dominated by the surface emission of hard jets. We predict the nuclear modification factor R^LHC AA - 0.15 in central Pb-Pb collisions at LHC. The study shows that the factorization model can be used to describe the centrality dependence of nuclear modification factor of the high transverse momentum particles produced in heavy ion collisions at both RHIC and LHC.     

K介子协变动力学及其准粒子模型的性质

简要综述了中高能重离子碰撞中K介子的产生及研究进展。重点介绍了K介子协变动力学模型, 并在此框架内分析了中高能重离子碰撞中K+介子以及与其伴随产生的Λ超子的集体流特征。 结果表明: 协变动力学模型能够很好地给出K+介子和Λ超子的微分直接流。 相对而言, 软势给出的集体流与实验值符合更好。同时, 通过对不同输运模型中K介子准粒子模型的基本属性进行对比分析, 明确了协变动力学模型中K介子准粒子模型的质量及能量随核物质密度的变化特征, 以及周围核子的运动对于K介子基本属性的影响。In the present paper, we briefly review the progress in the study of kaon production in heavy\|ion collisions at intermediate and high energies and introduce the covariant kaon dynamics model. The collective flows of positively charged kaon and the lambda hyperon associated produced with kaon are studied in the framework of the dynamics. It shows that the directed differential flow of K+ meson and Λ hyperon can be reasonably reproduced in the covariant kaon dynamics model. The calculated results with soft equation of nuclear matter are in better agrement with experimental data. Meawhile, a detailed comparison of the properites of different quasi\|particle models in various transport model and the influence of nucleon’s movement on the effective mass and energy of the quasi\|particle in the covariant kaon dynamics model are discussed.     

Study on the method of mini-jet identification in relativistic heavy ion collisions

In this paper a set of methods identifying minijet from final state particles in the relativistic heavy ion collision events is established and the parameter dependence has been investigated in Au+Au collisions at √s= 200 GeV using a multiphase transport model (AMPT). It is found that the number of minijets reduces with the increasing of collision parameter and raises with the increasing of c.m energy. Furthermore, we analyze the rapidity and momentum distribution inside minijets identified using this method.     

Nonlinear Effect on Effective Mass of Kaon

The study of hardron properties in dense medium crekted in relativistic heavy ion collision is a subject of considerable current interest. Of particular importance is the modification of kaon properties in-medium. The knowledge is useful for our understanding of both chiral symmetry restoration in dense matter and the properties of the dense nuclear matter existing in neutron stars.     

Medium Density and Parton Energy Loss in Gold-Gold Collisions from the Recombination Model

The pion production at mid-rapidity in gold-gold collisions at √s = 200 GeV is investigated by the parton recombination model. The density of the hot medium produced in the collisions and the hard parton energy loss effect are obtained by fitting the experimental data. Both of them are found to have power-law dependence on the number of binary collisions. The implication of such dependence on the nuclear modification factor is discussed.     

Excitation Mechanism of C60^r＋ Ions

Citation of the C60^4 is the same in the two collisions. The strong C peak produced in Ar^ -C60 must be due to the elastic collisions (nuclear stopping), because the Ar is heavy enough to knock out the C^ from C60 molecule. In general, the excitation energy depends on the projectile velocity, charge, and mass. Direct vibronic excitation by elastic collisions (nuclear stopping) is predicted for slow heavy ions, while the electronic excitation (electronic stopping) is dominant for fast ions[1]. For example, Schlatholter, et al.[2] found a strong velocity effect in collisions of He^ with fullerene in the velocity range from 0.1 to 1 a.u. With increasing velocity, the C2 evaporation process decreases and the multi-fragmentation is linearly increasing.     

Cross Sections of Barium Isotopes in Interaction of 60 MeV／u ^18O with Natural Uranium

The reactions induced by heavy ions lower than 10 MeV/u have been studied widely. Their reaction mechanism has been also understood in more detail. The contribution to the reaction cross sections in the low energy reactions comes mainly from complex nuclei and deep inelastic process. Early studies mainly focused on the nuclear collisions of low and high energies. In the recent years, great attention has been paid on the intermediate energy heavy ion collisions. Among them measurements of the cross sections and recoiling properties for the target fragmentation products have been applied widely to study the mechanism of the nuclear reactions induced by the intermediate energy heavy ions. But there are a few papers on raodioehemieal studies in the intermediate energy region up to now.     

Differential Directed Flow of K+ Meson within Covariant Kaon Dynamics

The collective flow of positive charged kaons in heavy ion reactions at SIS energy is investigated within the frame of covariant kann dynamics. The theoretical results calculated by using quantum molecular dynamics show that the rapidity distribution of K^＋ mesons is more sensitive to the nuclear equation of state than the differential directed flow. The contribution of various K^＋ production reaction channels to the rapidity distribution of the K^＋ is also analysed in detail. The results indicate that the rapidity distribution of K^＋ mesons is mainly from the contribution of the N-△ and N-N channel. This means that the delta resonance state plays a predominantly important role for the K^＋ subthreshold production.     

Transverse momentum and transverse mass distributions of charged hadrons produced in Au--Au collisions at high energies

The transverse momentum distribution and the transverse mass distribution of charged hadrons produced in nucleus nucleus collisions at high energies are described by using a two-cylinder model. The results calculated by the model are compared and found to be in agreement with the experimental data of the STAR and E895 Collaborations, measured in A~Au collisions at the relativistic heavy ion collider （RHIC） and alternating-gradient synchrotron （AGS） energies, respectively. In the energy range concerned, the excitation degree of emission source close to the central axis of cylinders increases obviously with the collision centrality and incident energy increasing, but it does not show any obvious change with the increase of the （pseudo）rapidity in central collisions. The excitation degree of emission source close to the side-surface of cylinders does not show any obvious change with the collision centrality, the （pseudo）rapidity, and the incident energy increasing.     

Roles of N?→NN and πN→? Reactions in Heavy-Ion Collisions at Intermediate Energies

Within the framework of the isospin-dependent transport model, the roles of the reactions N? → NN and πN→ ? are investigated through simulating heavy-ion collisions at 1000 MeV/nucleon. The absorption process N? → NN plays an important role for heavy impact systems and small impact parameters than for light impact systems and large impact parameters. The resorption process πN→ ? is of importance for heavy impact systems and large impact parameters than for light impact systems and small impact parameters. Thus the influences of the reaction N? → N N(πN→ ?) on pion production dynamics can be neglected in heavy-ion collisions for smaller(larger) impact parameters and light systems. It is the reaction πN→ ? that causes the anti-correlation of pions and nucleons in the rapidity dependence of the directed flow.     

Transverse Momentum and Rapidity Distributions of Φ Mesons Produced in Pb-Pb Collisions at SPS Energies

To investigate the excitation degree of the interacting system and the penetrating power of the projectile nucleus and to understand their dependences on incident energy, the transverse momentum and rapidity distributions of particles produced in nucleus-nucleus collisions at high energies are studied by using a multisource ideal gas model. The calculated results are compared with the most recent NA49 experimental data of φ mesons produced in Pb-Pb collisions at the Super Proton Synchrotron （SPS） energies.     

Application of the HKS in the identification of kaons produced in the reaction （e,e＇K^＋）

At Jefferson Laboratory the experiment E02-017 was carried out to investigate the fission associated with kaons in the hypernuclei-producing interaction p（e,K^＋e＇）A. The newly installed high resolution kaon spectrometer （HKS） in Hall C was used as a key instrument to identify kaons. This paper introduces the HKS hardware and describes the way the kaons are identified. Maintaining most of the kaons （nearly 100%） in the data, HKS identifies kaons with a purity of -67% in this experiment. The resolution of the kaon target time reconstructed by HKS reaches 0.42 ns.     

Gluon saturation and baryon stopping in the SPS, RHIC, and LHC energy regions

A new geometrical scaling method with a gluon saturation rapidity limit is proposed to study the gluon saturation feature of the central rapidity region of relativistic nuclear collisions. The net-baryon number is essentially transported by valence quarks that probe the saturation regime in the target by multiple scattering. We take advantage of the gluon saturation model with geometric scaling of the rapidity limit to investigate net baryon distributions, nuclear stopping power and gluon saturation features in the SPS and RHIC energy regions. Predictions for net-baryon rapidity distributions, mean rapidity loss and gluon saturation feature in central Pb+Pb collisions at the LHC are made in this paper.