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.     

Large mass dilepton production from jet-dilepton conversion in the quark-gluon plasma

We calculate the production of large mass dileptons from the passage of jets passing through the quark-gluon plasma. Using the relativistic kinetic theory, we rigorously derive the production rate for the jet-dilepton conversion in the hot medium. The jet-dilepton conversion is compared with the thermal dilepton emission and the Drell-Yan process. The contribution of the jet-dilepton conversion is not prominent for all values of the invariant mass M, and the Drell-Yan process is found to dominate over the thermal dilepton emission and the jet-dilepton conversion for M>2.5 GeV at RHIC. The jet-dilepton conversion is the dominant source of large mass dileptons in the range of 4 GeV<M<10 GeV at LHC.     

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.     

膨胀QGP的热双轻子产生(英文)

研究了QGP中次级热双轻子的产生。在RHIC能区, 次级热双轻子的产生在低质量范围0.2 GeV     

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.     

Dilepton from Passage of Jets Through Spherical Expanding QGP

We calculate the large mass dileptons production from the jet-dilepton conversion in spherical expanding quark-gluon plasma at Relativistic Heavy Ion Collider (RHIC) and Large Hadron Collider (LHC) energies. The jet-dilepton production exceeds the thermal and Drell-Yan dilepton production in the large mass region of 4.5 GeV< M< 5.5 GeV and 7 GeV< M< 9 GeV in central Pb+Pb collisions at √s_NN=2.76 TeV and 5.5 TeV, respectively. We present the solution of (1+3)-dimensional fluid hydrodynamics with spherical symmetry. We find that the transverse flow of the QGP leads to a rapid cooling of the fire ball and suppression of the jet-dilepton conversion. The suppression is also evident at intermediate and large mass at LHC energies. The energy loss of the jet-dilepton conversion is concerned.     

Dilepton from Passage of Jets Through Spherical Expanding QGP

We calculate the large mass dileptons production from the jet-dilepton conversion in spherical expanding quark-gluon plasma at Relativistic Heavy Ion Collider(RHIC) and Large Hadron Collider(LHC) energies.The jetdilepton production exceeds the thermal and Drell Yan dilepton production in the large mass region of 4.5 GeVM 5.5 GeV and 7 GeV M 9 GeV in central Pb+Pb collisions at SNNS~(1/2)=2.76 TeV and 5.5 TeV,respectively.We present the solution of(1+3)-dimensional fluid hydrodynamics with spherical symmetry.We find that the transverse flow of the QGP leads to a rapid cooling of the fire ball and suppression of the jet-dilepton conversion.The suppression is also evident at intermediate and large mass at LHC energies.The energy loss of the jet-dilepton conversion is concerned.     

Measuring quark-gluon-plasma thermalization time with dileptons

We calculate the medium dilepton yield from a quark-gluon plasma which has a time-dependent local momentum-space anisotropy. A phenomenological model for the hard momentum scale, p(hard)(tau), and plasma anisotropy parameter, xi(tau), is constructed which interpolates between longitudinal free streaming at early times (tautau(iso)). We show that high-energy dilepton production is sensitive to the plasma isotropization time, tau(iso), and can therefore be used to experimentally determine the time of onset for hydrodynamic expansion of a quark-gluon plasma and the magnitude of expected early-time momentum-space anisotropies.     

Correlations between transverse energy production and the Drell-Yan process in heavy ion collisions at high energy

The expression for the Drell-Yan cross section is presented which takes into account the geometry of heavy ion collisions. The Drell-Yan cross section is shown to be proportional to the transverse energy produced within a fixed rapidity interval. A dependence steeper than linear of the cross section for production of dileptons with masses larger than about 2 GeV on the transverse energy in a given rapidity bin would be a clear-cut signal for the formation of the quark-gluon plasma.     

Dilepton production from ρ-mesons in a quark-gluon plasma

Assuming that ρ-mesons exist in a quark-gluon plasma at temperatures close to the QCD phase transition, we calculate the dilepton production rate from q-ˉq annihilation via a ρ-meson state using Vector Meson Dominance. The result is compared to the rates from direct q-ˉq annihilation and from π⁺-π⁻ annihilation. Furthermore we discuss the suppression of low mass dileptons if the quarks assume an effective mass in the quark-gluon plasma. Received: 8 September 1999 / Revised version: 22 October 1999     

Low-mass dileptons at high momenta in ultra-relativistic heavy-ion collisions

We calculate the emission rate of low-mass dileptons at high momenta from a quark-gluon plasma. We find a large enhancement compared with the naive Born rate. Numerical estimates for relativistic heavy ions collisions at RHIC and LHC suggest, however, that the thermal signal is dominated by the background coming from meson decays and from hadronic bremsstrahlung.     

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.     

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     

Baryon deceleration and partonic plasma creation by strong chromofields in ultrarelativistic heavy-ion collisions

Strong chromofields generated at early stages of ultrarelativistic nuclear collisions may explain not only creation of the quark-gluon plasma but also collective deceleration of net baryons. This is demonstrated by solving classical equations of motion for baryonic slabs under the action of a time-dependent chromofield. We have studied sensitivity of the slab trajectories and their final rapidities to the initial strength and decay time of the chromofield, as well as to the back reaction of the produced plasma. By proper choice of the initial chromofield energy density we can reproduce significant baryon stopping, an average rapidity loss of about two units, observed for Au + Au collisions at RHIC. Using a Bjorken-like hydrodynamical model with the particle production source, we also study the evolution of partonic plasma produced as the result of the chromofield decay. Due to the delayed formation and expansion of plasma its maximum energy density is significantly lower than the initial energy density of the chromofield. It is shown that the fluctuations of the chromofield due to the stochastic distribution of color charges help to populate the midrapidity region in the net-baryon distribution. To fit the midrapidity data we need the chromofields with initial energy densities in the range of 30 to 60 GeV/fm³. Predictions of baryon stopping for Pb + Pb collisions at LHC energies are made.     

Baryon recoil and the fragmentation regions in ultra-relativistic nuclear collisions

The maximum baryon and energy densities reached in the fragmentation regions of nuclear collisions are estimated with a new hydrodynamical model. Unlike previous models where recoil is included as a source term for the baryon current, in our model the baryon current is strictly conserved. The parameters of the model are furthermore adjusted to take into account the large baryon rapidity shifts observed recently in p + A → p + X. The implications for the production of high baryon density quark-gluon plasmas are discussed.     

Photons,Dileptons and Hadrons Produced by Quark-Gluon Plasma

Altarelli-Parisi equations in perturbative QCD are applied to getting evolution equations of quark-gluon plasma. The equations describe the cooling process of quark-gluon plasma by emitting photons. The numbers of observable photons and dileptons are calculated directly from these equations. The cooled quark-gluon plasma hadronizes and the production rates of hadrons are calculated with separable scalar confinement potentials.     

Photon production from baryon rich quark-gluon plasma

We study high energy photon production from a quark-gluon plasma at finite baryon density. We find that the photon production spectrum from the quark-gluon plasma maintained at constant temperature is only mildly dependent on the quark chemical potential.     

Sensitivity of electromagnetic spectra to equation of state and initial energy density in the Pb + Pb collisions at SPS

We study Pb + Pb collisions at 158 A GeV/c using hydrodynamical approach. We test different equations of state (EoSs) and different initial conditions and show that there are more than one initial state for each EoS which reproduce the observed hadronic spectra. We also find that different equations of state favor different freeze-out temperature. Simultaneously we calculate the thermal dilepton and photon spectra for each EoS and initial state. We compare the dilepton mass spectrum to data measured by the CERES collaboration and find that the differences in spectra obtained using different EoSs and initial states are not resolvable within the current experimental resolution. However, at invariant masses over 2 GeV the difference in the yield due to various initial states is close to an order of magnitude. We also study the rapidity distribution of lepton pairs and find that for masses around 800 MeV the shape of the distribution depends strongly on the EoS.     

Zero-Density Phase Transition to Quark-Gluon Plasma and the Relativistic Finite Baryon Volume Effect in Hadronic Matter

We examine the role of relativistic finite baryon volume effect in the phase transition between hadronic matter and quark-gluon plasma at vanishing baryon density. It is found that the appearance of abnormal state at high temperature may enhance the baryon-antibaryon excitation, which has large influence on the quark-gluon plasma formation. The numerical results show that the occurence of this phase transition depends on how to extrapolate the nucleon-scalar meson coupling constant to the baryonic resonance-scalar meson coupling.     

Charm production in a quark-gluon plasma

A calculation is made for charm quark production in a longitudinally expanding quark-gluon plasma. A comparison is made with hadronic charm production in ultra-relativistic nuclear collisions assuming an extrapolation from p-p collisions and no plasma formation. The charm yield from a QGP begins to dominate purely hadronic production for plasma temperatures above 315–440 MeV, depending on the bombarding energy of the colliding nuclei and the value assumed for the charm quark mass. Implications for plasma signals, most notably dilepton emission and J/ψ suppression, are discussed.