夸克-胶子物质的特征双轻子分布

运用相对论性的流体力学模型,研究了夸克-胶子火球的双轻子产生,发现随着初始温度的增加零重子的夸克-胶子火球的双轻子总产额在一个平台后单调地上升,而随着初始重子密度的增加富重子的夸克-胶子火球的双轻子总产额呈现一个样.夸克-胶子物质在碰撞中形成的特征可在将来的CERN和Brookhaven实验中得到检验.     

化学非平衡夸克-胶子物质中等质量双轻子的产生

研究了正在进行化学平衡的富重子夸克-胶子物质的双轻子产生，发现由于产生在RHIC能量 的化学非平衡的富重子夸克-胶子物质冷却慢和高的初始温度，导致中等质量双轻子产生重 大增强.因此，中等质量双轻子的增强可以是夸克-胶子物质形成的信号.同时，这个增强能 补偿由于初始夸克化学势增加引起的双轻子抑制，因而双轻子产额的抑制不再是夸克-胶子 物质产生的信号. 关键词： 化学非平衡夸克-胶子物质 热粲夸克 双轻子     

膨胀的热夸克胶子物质的中等质量双轻子的增强

基于一个描述夸克胶子火柱演化的相对论流体力学模型,研究了夸克相、强子相互作用以及非热过程(DrellYan对、粲强子衰变)的中等质量双轻子的产生.发现由于相边对夸克胶子物质演化的影响和RHIC能量核碰撞产生的夸克胶子物质具有高的初始温度,夸克相对双轻子的贡献显著增强,比那些来自强子相互作用的贡献重要,甚至能与来自非热的贡献比较.表明中等质量双轻子的增强是一个在核碰撞中产生了夸克胶子物质的可能信号. 关键词： 夸克-胶子物质 双轻子增强 相对论流体力学模型     

膨胀的热的富重子夸克–胶子物质的双轻子产生

从核完全阻止的假定出发,基于一个相对论性流体力学模型,研究了富重子夸克-胶子物质的双轻子产生,发现随着入射能量的增加,在双轻子总产额中出现一个标志富重子夸克-胶子物质形成的特征平台,这样显著的特征可在CEEN和Brookhaven即将开展的实验中得到检验.     

膨胀的热的富重子夸克─胶子物质的双轻子产生的抑制

从完全核阻止的假定出发基于3+1维RHE研究了双轻子谱,并得到结论:如果在极端相对论性原子核碰撞中富重子的夸克-胶子物质真地产生了,那么随着初始重子密度的增加,在不变质量2mπ和1GeV之间双轻子的产生将会显示出强烈的抑制,而且将有一个反常的峰出现在不变质量0.75GeV附近.这些预言可以在CERN和Brookhaven即将开展的实验中得到检验.     

胶子非弹性散射过程对夸克胶子等离子体中双轻子产生的影响

双轻子是研究夸克物质的形成和性质的重要探针.本文基于化学平衡化的黏滞性夸克胶子等离子体演化模型,计算了相对论重离子碰撞能量下金-金对心碰撞形成的夸克胶子等离子体中的双轻子产额.在黏滞性计算中加入了胶子非弹性散射过程对黏滞系数的贡献.相较仅考虑夸克和胶子弹性散射的情况,双轻子的产额有较明显的降低.这表明在黏滞系数中加入胶子非弹性散射的贡献使得系统的演化过程加快,演化时间变短.     

夸克-胶子等离子体在相对论性核-核碰撞中形成的一种信号

从热力学关系,计算来自相对论性核-核碰撞的富重子夸克-胶子等离子体的初值.接着基于(3+1)维相对论性流体力学模型研究了系统的双轻子产生.发现随着碰撞核入射能量的增加,一个标志夸克-胶子等离子体形成的特征平台出现在双轻子的总产额中.这样的特征可在CERN和Brookhaven未来的实验中得到检验. 关键词：     

膨胀的热的富重子夸克─胶子物质的双轻子产生的抑制

从完全核阻止的假定出发基于３＋１维ＲＨＥ研究了双轻子谱，并得到结论：如果在极端相对论性原子核碰撞中富重子的夸克－胶子物质真地产生了，那么随着初始重子密度的增加，在不变质量２ｍπ和１ＧｅＶ之间双轻子的产生将会显示出强烈的抑制，而且将有一个反常的峰出现在不变质量０．７５ＧｅＶ附近．这些预言可以在ＣＥＲＮ和Ｂｒｏｏｋｈａｖｅｎ即将开展的实验中得到检验．     

夸克–胶子的等离子体在核–核碰撞中形成的信号

从热力学关系,得到来自相对论核碰撞形成的夸克胶子系统的初始值.基于这些初始值,在相对论流体力学模型下研究了双轻子的产生,发现随着入射能量的增加,一个标志夸克胶子等离子体形成的特征平台出现在总产额中.这些特征可在CERN(西欧中心)和Brookhaven未来的实验中得到检验.     

富重子夸克–胶子物质双轻子产生的快度依赖

考虑Drell–Yan本底,基于相对论性流体力学模型,研究了来自¹⁹⁷Au十¹⁹⁷Au中心碰撞的富重子夸克–胶子物质的双轻子产生的快度依赖.发现随着快度的增加,双轻子产额呈现出强烈的抑制.这个标志富重子夸克–胶子物质形成的特征能够在CERN和Brookhaven将来的实验中得到检验.     

夸克-胶子的等离子体在核-核碰撞中形成的信号

从热力学关系,得到来自相对论核碰撞形成的夸克－胶子系统的初始值,基于这些初始值,在相对论流体力学模型下研究了双轻子的产生,发现随着入射能量的增加,一个标志夸克－胶子等离子体形成的特征平台出现的总产额中,这些特上可在ＣＥＲＮ（西欧中心）和Ｂｒｏｏｋｈａｖｅｎ未来的实验中得到检验。     

Dilepton production in an expanding baryon-rich quark-gluon fireball

From the full stopping scenario, the dilepton production in a baryon-rich quark-gluon fireball has been studied based on a relativistic hydrodynamic model. Due to the influence of the phase boundary on the evolution of the system, the quark phase gives the dominant contribution to the dilepton spectrum. In particular, with increasing initial baryon density, the total dilepton yield first rapidly rises when the initial hadronic system goes to the initial quark system, then goes down owing to the suppression of the dilepton production, thus making a characteristic peak signaling the formation of the baryon-rich quark-gluon matter which appears in the total yield. These characteristics can be tested in future experiments at CERN and Brookhaven.     

Finding charm at RHIC

Dileptons produced by hard scatterings, such as heavy quark decays and the Drell-Yan mechanism, probe the gluon and sea quark distributions in hadrons. In nucleus-nucleus collisions, these processes are the thermal ‘back-ground’. To determine the magnitude and behavior of this background, we calculate the hard scattering contribution to next to leading order in perturbative QCD at RHIC. We compare these results to optimistic estimates of thermal dilepton production and find that initial charm production is dominant. However, experimental cuts can reduce the charm background, enhancing thermal information.     

The Density Effects on the Thermal Production Rate of Dilepton in QGP

In the framework of the thermo field dynamics (TFD) we discuss thermal production of dileptons in quark gluon plasma (QGP) of finite temperature and density up to the first order of QCD correction. We show that the temperature effect to the thermal production rate is rather different from that of the chemical potential, in fact, they give rise to opposite effects which may influence the observation of the dilepton production in QGP.     

Dilepton Spectrum from An Expanding Hot Nuclear Matter

In this paper the dilepton spectrum from an expanding hot nuclear matter is studied.Comparing with the spectrum from hot quark matter,we find that they are quite different.Especially the former with respect to the initial temperature or particle density is monotonic,the latter is non-monotonic.This may serve as theoretical examination for the production of quark phase transition.     

QCD corrections to the Drell-Yan mechanism and the pion structure function

We compute the differential cross section dσ/dQ² dy for lepton pair production up to first order in the strong coupling constant α_s. We show that, in the region where the theory applies and where the statistical accuracy of the experiments is good, the ratio of the QCD correction to the Drell-Yan cross section is approximately constant, and that its magnitude is in good agreement with the results of the CERN-NA3 experiment. We thus show that, within the framework of this first-order calculation, the shape of the pion structure function extracted from dilepton production in πp collisions is approximately correct. We also comment on the average transverse momentum of the dilepton due to gluon or quark recoil.     

Plasma production and thermalisation in a strong field

Aspects of the formation and equilibration of a quark–gluon plasma are explored using a quantum kinetic equation, which involves a non-Markovian, Abelian source term for quark and antiquark production and, for the collision term, a relaxation time approximation that defines a time-dependent quasi-equilibrium temperature and collective velocity. The strong Abelian field is determined via the simultaneous solution of Maxwell's equation. A particular feature of this approach is the appearance of plasma oscillations in all thermodynamic observables. Their presence can lead to a sharp increase in the time-integrated dilepton yield, although a rapid expansion of the plasma may eliminate this signal. Received: 27 July 2001 / Published online: 21 November 2001     

The extent of strangeness equilibration in quark gluon plasma

The evolution and production of strangeness from chemically equilibrating and transversely expanding quark gluon plasma which may be formed in the wake of relativistic heavy-ion collisions is studied with initial conditions obtained from the self screened parton cascade (SSPC) model. The extent of partonic equilibration increases almost linearly with the square of the initial energy density, which can then be scaled with the number of participants.