Heavy-flavour spectra in high-energy nucleus–nucleus collisions

The propagation of the heavy quarks produced in relativistic nucleus–nucleus collisions at RHIC and LHC is studied within the framework of Langevin dynamics in the background of an expanding deconfined medium described by ideal and viscous hydrodynamics. The transport coefficients entering into the relativistic Langevin equation are evaluated by matching the hard-thermal-loop result for soft collisions with a perturbative QCD calculation for hard scatterings. The heavy-quark spectra thus obtained are employed to compute the differential cross sections, the nuclear modification factors R _AA and the elliptic-flow coefficients v ₂ of electrons from heavy-flavor decay.     

Multiparticle correlations in resonance-matter formation

The effect of multiparticle correlations on resonance and pion populations, in relativistic nuclear reactions, is calculated in the context of an intranuclear cascade model which includes N-body (N > 2) collisional processes. The resonance-matter population present in the highly-compressed phase of nucleus-nucleus collisions is investigated, in reactions between different intermediate-mass nuclear systems. Received: 29 December 1998 / Revised version: 20 December 1999     

Multifragmentation calculated with relativistic forces

A saturating hamiltonian is presented in a relativistically covariant formalism. The interaction is described by scalar and vector mesons, with coupling strengths adjusted to nuclear matter. No explicit density dependence is assumed and the momentum dependence results from the relativistic expansion. The hamiltonian is applied in a QMD calculation to determine the fragment distribution in O+Br collisions at different energies (50–200 Me V/u) to test the applicability of the model at low energies. The results are compared with experiment and with previous non-relativistic calculations.     

Angular pattern of minijet transverse energy flow in hadron and nuclear collisions

The azimuthal asymmetry of a minijet system produced at the early stage of nucleon–nucleon and nuclear collisions in a central rapidity window is studied. We show that in pp collisions the minijet transverse energy production in a central rapidity window is essentially unbalanced in the azimuth due to asymmetric contributions in which only one minijet hits the acceptance window. We further study the angular pattern of the transverse energy flow generated by the semihard degrees of freedom at the early stage of high energy nuclear collisions and its dependence on the number of semihard collisions in the models both including and neglecting soft contributions to the inelastic cross section at RHIC and LHC energies as well as on the choice of the infrared cutoff. Received: 19 January 1999 / Revised version: 18 February 2000 / Published online: 26 July 2000     

Evidence of self-affine multiplicity fluctuation of target residues in ^84Kr-AgBr interactions at 1.7 AGeV

Self-affine multiplicity scaling is investigated in the framework of a two-dimensional factorial moment methodology using the concept of the Hurst exponent （H）. Analyzing the experimental data of target evaporated fragments emitted in ^84Kr-AgBr interactions at 1.7 AGeV revealed that the best power law behavior is exhibited for H = 0.3 indicating a self-arlene multiplicity fluctuation pattern. A signal of multifractality is also observed from knowledge of the anomalous fractal dimension dq extracted from the intermittency exponent aq of the anisotropic phase space scenario.     

Flavor-dependent photoproduction in heavy-ion collisions

Strong electromagnetic fields produced in the non-central heavy-ion collisions can induce vector meson photoproduction. In this paper, we study the photoproduction J/ψ and φ mesons in the relativistic heavy-ion collision from ultra-peripheral nuclear collisions to peripheral hadronic heavy ion collisions. And then include both initial hadronic production and thermal production in quark-gluon plasma (QGP). We find, for the charm anti-charm bound state J/ψ, the photoproduced J/ψs are mainly in the very low momentum region and clearly exceed the hadronic production. However, considering the thermal production of strange quark anti-quark pairs in QGP produced in relativistic heavy-ion collisions, the photoproduced φ is usually smaller than the thermal production and only evident at very peripheral collisions as even their photoproduction is much larger than J/ψ.     

Multiplicities of forward-backward particles in ^16O-emulsion interactions at 4.5 AGeV/c

An exclusive study of the characteristics of interactions accompanied by backward emission（θlab 90°） of shower and grey particles in collisions of a 4.5 AGeV/c ^16O beam with emulsion nuclei is carried out. The experimental multiplicity distributions of different particles emitted in the forward（θlab 〈 90°） and backward hemispheres due to the interactions with the two emulsion components（CNO,AgBr） are presented and analyzed. The correlations between the different emitted particles are also investigated. The results indicate that there are signatures for a collective mechanism,which plays a role in the production of particles in the backward hemisphere. Hence,the backward multiplicity distribution of the emitted shower and grey particles at 4.5 AGeV/c incident momentum can be represented by a decay exponential law formula independent of the projectile size. The exponent of the power was found to increase with decreasing target size. The experimental data favor the idea that the backward particles were emitted due to the decay of the system in the latter stages of the reactions.     

Summary of ISNP2K

This is a brief summary of the ISNP2K (International Symposium on Nuclear Physics, 2000). Many interesting works were presented on new developments and perspectives of nuclear physics in the plenary and poster sessions. Subjects discussed are 1) high temperature and high density nuclei, new QGP phases and relativistic HI collisions, 2) new degrees of freedoms studied by medium energy reactions, 3) exotic nuclei with large isospin, large A, high J and high E _x , 4) new dynamical properties of many body nucleon systems, 5) neutrino nuclear physics and neutrons for astroparticle physics, and 6) new accelerators and new applications. ISNP2K with extensive discussions on nuclear physics frontiers at the turning point from 2000 to 2001 provides a good bridge to the new century.     

Multifragmentation in peripheral collisions of relativistic heavy ions

The breakup of heavy ions in peripheral collisions at relativistic energies offers a rich field of nuclear studies such as the investigation of nuclear structure, the production of energetic beams of exotic nuclei and studies of hot nuclear matter. Examples of recent experimental results obtained at GSI Darmstadt with the heavy ion synchrotron SIS will be discussed with emphasis on the nuclear breakup in the domain from distant collisions without nuclear contact by Coulomb excitation, to peripheral collisions with increasing overlap between projectile and target. The production of relativistic beams of exotic nuclei by fragmentation opens up a new area of nuclear structure research.Invited lecture given at the International School-Workshop Relativistic Heavy-Ion Physics, Prague (Czech Republic), 19–23 September 1994.     

Electromagnetic processes in relativistic heavy ion collisions

Electromagnetic effects in relativistic heavy ion collisions with impact parameter larger than the sum of the nuclear radii are studied using the virtual photon method. With increasing value of the relativistic parameter γ the hardness of the virtual photon spectrum increases. This leads to interesting new effects which will also have to be considered in the design of future relativistic heavy ion machines and experiments. The excitation of high-lying giant E1 and E2 multipole resonances is calculated as well as electromagnetic pion production. Coulomb bremsstrahlung is calculated and compared to the bremsstrahlung emitted in the more violent central nuclear collisions. K-shell ionization and electron-positron pair production is studied. The latter process has a very large cross section for heavy ions and contributes significantly to the stopping power of relativistic heavy ions in a dense medium.     

Constraints for the nuclear sea quark distributions from the Drell–Yan process at the SPS

Nuclear modifications to the Drell–Yan dilepton production cross sections in and collisions in the leading twist approximation are caused by nuclear effects in the parton distributions of bound nucleons. For non-isoscalar nuclei, isospin corrections must also be considered. We calculate these effects for and Pb+Pb collisions at CERN SPS energies. Our goal is to place constraints on nuclear effects in sea quark distributions in the region . We show that the net nuclear corrections remain small for collisions at GeV. However, in collisions at GeV, effects of are predicted at large M. The data collected by the NA50 collaboration could thus be used to constrain the nuclear effects in the sea quark distributions in the region of the EMC effect, . Received: 6 October 2000 / Revised version: 2 July 2001 / Published online: 19 September 2001     

相对论重离子碰撞中的重味产生

重味粒子是新的物质形态——夸克胶子等离子体的敏感探针。 利用相对论流体力学描述夸克胶子等离子体的时空演化, 采用输运方程模拟重味粒子在夸克胶子等离子体中的运动, 既考虑重味粒子的热胶子离解, 也通过细致平衡原理包含重味粒子在热密媒质中的重产生。 正是由于离解与重产生之间的竞争以及竞争对于碰撞能量、 横动量和快度的依赖性, 自然解释了在RHIC能区的J/ψ疑难, 预言了在LHC能区由于重产生取得主导地位, J/ψ的核修正因子在中心和半中心碰撞中将随着参与反应核子数的增大而升高, 同时其平均横动量会受到强烈的压低。 Heavy quarkonium is a sensitive signature of the new state of matter-quark gluon plasma produced in high energy nuclear collisions. We describe the space time evolution of the quark gluon plasma by relativistic hydrodynamic equations and the quarkonium motion by transport equation. We found that the competition between the gluon dissociation and regeneration can explain naturally the J/ψ puzzles at RHIC energy. We predict the increase of the nuclear modification factor in semi central and central collisions and the related transverse momentum suppression at LHC energy.     

Radiative and collisional energy loss,and photon-tagged jets at RHIC

The suppression of single jets at high transverse momenta in a quark–gluon plasma is studied at RHIC energies, and the additional information provided by a photon tag is included. The energy loss of hard jets traversing through the medium is evaluated in the AMY formalism, by consistently taking into account the contributions from radiative events and from elastic collisions at leading order in the coupling. The strongly interacting medium in these collisions is modeled with (3+1)-dimensional ideal relativistic hydrodynamics. Putting these ingredients together with a complete set of photon-production processes, we present a calculation of the nuclear modification of single jets and photon-tagged jets at RHIC.     

Search for Exotic Strange Dibaryon in Relativistic Heavy Ion Collisions

The exotic strange dibaryon particle (ΩΩ)0 with S = -6 can be produced in relativistic heavy ion collisions. The yields of this kind of exotic strange dibaryon particles can increase signitlcantly soon as the formation of QGP does exhibit after the collision. If there is no phase transition after the collision, the upper bound of the production of this diomega can be estimated from the free hadronic gas model for nuclear matter. The relative yield ratio of diomega to deuteron is less than 0.000205, this means that if there is no QGP creation it is difficult to observe the production of diomega in relativistic heavy ion collisions.     

Isospin effects on subthreshold kaon production at intermediate energies

We show that in collisions with neutron-rich heavy ions at energies around the production threshold K0 and K+ yields probe the isospin-dependent part of the nuclear equation of state at high baryon densities. In particular, we suggest the K0/K+ ratio as a promising observable. Results obtained in a covariant relativistic transport approach are presented for Au+Au collisions at 0.8-1.8A GeV. The focus is put on the equation of state influence which goes beyond the collision-cascade picture. The isovector part of the in-medium interaction affects the kaon multiplicities via two mechanisms: (i) a symmetry potential effect, i.e., a larger neutron repulsion in n-rich systems, and (ii) a threshold effect, due to the change in the self-energies of the particles involved in inelastic processes. Genuine relativistic contributions are revealed that could allow one to directly "measure" the Lorentz structure of the effective isovector interaction.     

High energy nuclear collisions: Theory overview

We review some basic concepts of relativistic heavy-ion physics and discuss our understanding of some key results from the experimental program at the relativistic heavy-ion collider (RHIC). We focus in particular on the early time dynamics of nuclear collisions, some result from lattice QCD, hard probes and photons.     

Low mass dilepton production in relativistic heavy ion collisions

Mechanisms of formation for low mass dilepton excess observed in the relativistic heavy ion collisions are considered. The experimental data are reviewed. In addition to discussing the standard mechanisms of dilepton production specific to the collisions of relativistic nuclei (the pion annihilation in the hadron-gas stage and the quark-antiquark annihilation in the quark-gluon phase), the mechanism of dilepton production in the mixed phase of nuclear matter is proposed, and its contribution to the low mass dilepton spectrum is estimated. In addition, the first-order corrections in the strong-interaction coupling constant to the dilepton production in the parton medium and the nonperturbative approaches are considered.     

First beams and experiments at the nuclotron

The new heavy ion superconducting synchrotron - Nuclotron was put into operation and the pilot physics results on relativistic nuclear collisions were obtained.