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     

化学非平衡夸克–胶子等离子体中的双轻子产生

研究了正在进行化学平衡的具有有限重子密度的夸克–胶子等离子体系统的演化和双轻子产生.结果发现由于夸克相的寿命随初始夸克化学势的增加而增加,以及其他一些因素,如较高的初始温度、较大的胶子密度和较大的胶子聚变和夸克湮没反应截面,导致热粲夸克对双轻子产生提供了占统治的贡献.这个效应造成中等质量双轻子的重大增强.     

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：     

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.     

产生在夸克–胶子等离子体中的中等质量双轻子的增强

基于一个相对论流体力学模型,在夸克–胶子等离子体中具有中等质量双轻子的产生被研究.由于相边对夸克–胶子等离子体系统演化的影响和产生在RHIC能量的夸克–胶子等离子体系统有高的初始温度,夸克相的贡献变得比强子相互作用的贡献重要得多,甚至能与本底相比较.它表明这样的增强是夸克–胶子等离子体形成的一种信号.     

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.     

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     

柱形夸克胶子等离子体的2π干涉学检测

在2п干涉学中,对不同的п源2п,关联函数可以是不同的. 如果在相对论重离子碰撞中出现柱形夸克胶子等离子体,п介子将从柱形夸克胶子等离子体表面发射,此时2п关联函数将出现一种特殊的振荡行为.这种振荡行为可以用来探明夸克胶子等离子体的存在性,同时也是相对论重离子碰撞中出现夸克胶子等离子体的一个信号.     

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。     

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.     

Equilibration in quark gluon plasma

The hydrodynamic expansion rate of quark gluon plasma (QGP) is evaluated and compared with the scattering rate of quarks and gluons within the system. Partonic scattering rates evaluated within the ambit of perturbative Quantum Choromodynamics (pQCD) are found to be smaller than the expansion rate evaluated with ideal equation of state (EoS) for the QGP. This indicate that during the space-time evolution the system remains out of equilibrium. Enhancement of pQCD cross sections and a more realistic EoS keep the partons closer to the equilibrium.     

Sensitivity of dilepton angular distributions to the gluon spin

Previous work on properties of dilepton angular distributions which are independent of parton distribution functions is extended to include scalar gluons. For moderate dilepton transverse momentum and large mass, the three measurable coefficients are quite sensitive to the gluon spin. Results are presented for both the annihilation and Compton scattering processes.     

A new tool for the study of fundamental interactions: Parity-odd correlations in quark fragmentation

Parity-odd correlations among the fragmentation products of quarks should reveal the longitudinal polarization of these quarks. Possible applications of this idea include a new way to determine the Weinberg angle from data on neutrino reactions, a sensitive test of the quark-antiquark creation picture in e⁺e^? annihilation, a way to determine the weak coupling of hypothetical heavy particles to light quarks and a test for the parton-parton scattering model with elementary gluon exchange for high p⊥ events in nucleon-nucleon collisions.     

Diffractive production of dijets at HERA

We investigate the production of a quark-antiquark pair in diffractive photon-proton scattering, approximating soft pomeron exchange by the exchange of two nonperturbative gluons. In deep inelastic scattering at HERA, events with two jets and the scattered proton in the final state are predicted to be observable, with an important contribution from charm production. For photoproduction of light quark jets with high transverse momentum we find that both exchanged gluons must have a large invariant mass, so that the cross section is very small, whereas for charm quarks it is quite appreciable. From our calculation we also extract the quark structure function of the pomeron for the scaling variablez no too close to 0 or 1, finding a strong flavour dependence and a behaviour somewhat harder thanz(1?z) for light quarks.     

Signals of excited quarks and leptons

e⁺e^? annihilation to two photons (including beam polarization) and quark-antiquark annihilation to gluons are discussed as possible tools to investigate the existence (and handedness) of excited electrons and quarks. Properties of these particles can also be explored in eγ and ep colliders; production cross sections and the impact of these particles on structure functions are derived.     

On the glue content in heavy quarkonia

Starting with two coupled Bethe-Salpeter equations for the quark-antiquark, and for the quark-glue-antiquark component of the quarkonium, we solve the bound state equations perturbatively. The resulting admixture of glue can be partially understood in a semiclassical way; one has, however, to take care of the different use of time ordered versus retarded Green functions. Subtle questions concerning the precise definition of the equal time wave function arise, because the wave function for the Coulomb gluon is discontinuous with respect to the relative time of the gluon. A striking feature is that a one loop non-abelian graph contributes to the same order as tree graphs, because the couplings of transverse gluons in the tree graphs are suppressed in the non-relativistic bound state, while the higher order loop graph can couple to quarks via non-suppressed Coulomb gluons. We also calculate the amplitude for quark and antiquark at zero distance in the quark-glue-antiquark component of the P-state. This quantity is of importance for annihilation decays of P-states. It shows a remarkable compensation between the tree graph and the non-abelian loop graph contribution. An extension of our results to include non-perturbative effects is possible.Received: 24 April 2003, Revised: 4 June 2003, Published online: 20 August 2003     

Electromagnetic radiation from QGP with chromo-magnetic monopoles

We consider the radiation of photons from quarks scattering on color-magnetic monopoles in the Quark-Gluon Plasma. The calculation is performed in the classical, non-relativistic approximation and results are compared to photon emission from Coulomb scattering of quarks, known to provide a significant contribution to the photon emission rates from the QGP. The present study is a first step towards understanding whether this scattering process can give a sizable contribution to dilepton production in heavy-ion collisions.     

A non-plasma approach to the soft dilepton production inhA andAA collisions

We propose a method of evaluating the soft dilepton production rate in hadron-nucleus and nucleus-nucleus collisions at high energies based on summing the contributions from quark-antiquark systems (chains) created in individual hadron-nucleon interactions. The individual contributions are determined by using the square dependence of the soft dilepton production rate on hadron multiplicity predicted for hadron-hadron collisions by the soft-quarkannihilation model and observed recently inpp collisions at the CERN ISR. The possibility of additional contributions originating from the annihilation of quarks and antiquarks that belong to different chains is taken into account in a phenomenological way, which nevertheless enables to correlate different phenomena in soft dilepton production. More detailed predictions are given for proton-nucleus collisions at 200 GeV/c.