[en] In high-energy nuclear collisions, the new phase of the quark-gluon plasma is indicated by an anomalous increase in pressure, an excess of direct photon production, an excess of strangeness production, and an anomalous J/ψ suppression. We review these signatures and discuss how recent high-energy heavy-ion experiments at CERN are consistent with the production of the quark-gluon plasma in high-energy Pb+Pb collisions

[en] Many of the hadron-hadron cross sections required for the study of the dynamics of matter produced in relativistic heavy-ion collisions can be calculated using the quark-interchange model. Here we evaluate the loW--energy dissociation cross sections of J/ψ, ψ', χ, Υ, and Υ' in collision with π, ρ, and K, which are important for the interpretation of heavy-quarkonium suppression as a signature for the quark gluon plasma. These comover dissociation processes also contribute to heavy-quarkonium suppression, and must be understood and incorporated in simulations of heavy-ion collisions before QGP formation can be established through this signature

[en] Recent studies found that the (Pt/Co/Pt) trilayers can be used as a unit in combination with nonmagnetic or magnetic layer, X (X=Pd, Ag, Cu, and Ni), to enhance the perpendicular magnetic anisotropy of the films, reduce the Curie temperature, and alter the magneto-optical properties. The effects of intercalating Cr into Pd/Co multilayers on the magnetic and magneto-optical properties are studied in this article. The perpendicular magnetic anisotropy K_u and the coercivity H_c of the system decrease rapidly with increasing the Cr thickness (X_Cr) up to 0.4 nm, and change slightly when Cr thickness further increases. The dependence of the coercivity H_c on the Cr thickness, which obeys the law: H_c (X_Cr)=X_Cr^-2.66, indicates that the magnetization reversal is controlled by domain wall moving, mainly due to the interface roughness. Large decrease of the Kerr rotation θ_k of the Pd/Cr/Co multilayers compared with pure Pd/Co multilayers is also found in the wavelength ranging from 200 to 800 nm. As it is well known, the large anisotropy and Kerr rotation in Pd/Co system are mainly caused by the polarization of Pd atoms due to nearby Co atoms. As the intercalating of Cr layer between Pd and Co layer, the average polarization of Pd atoms will be reduced largely. As a matter of fact, the Cr atoms can also be polarized by nearby Co atoms, which, however, seems to take a minor effect on the anisotropy and Kerr rotation of the system. [copyright] 2001 American Institute of Physics

No abstract available

[en] The time-dependent Hartree-Fock approximation is approximately equivalent to a purely classical pseudoparticle simulation. In this simulation, a collection of pseudoparticles are introduced to discretize the phase space of spatial and momentum coordinates. The dynamics is completely determined by following the pseudoparticle trajectories which are the same as the trajectories of real particles moving in the self-consistent field. An application of these concepts to nearly-head-on heavy-ion collisions leads to a better understanding of the origin of the low-l fusion window obtained in the TDHF calculations

[en] We present numerical results for the dissociation cross sections of ground-state, orbitally- and radially-excited charmonia in collisions with light mesons. Our results are derived using the nonrelativistic quark model, so all parameters are determined by fits to the experimental meson spectrum. Examples of dissociation into both exclusive and inclusive final states are considered. The dissociation cross sections of several C=(+) charmonia may be of considerable importance for the study of heavy ion collisions, since these states are expected to be produced more copiously than the J/ψ. The relative importance of the productions of ground-state and orbitally-excited charmed mesons in a pion-charmonium collision is demonstrated through the √s-dependent charmonium dissociation cross sections

[en] The observed features of ψ' to J/ψ suppression in pA and nucleus-nucleus collisions can be explained in terms of a two-component absorption model. For the hard component of the absorption due to the interaction of the produced cc-bar systems with baryons at high relative energies, the absorption cross sections are insensitive to the radii of the cc-bar systems, as described by the Additive Quark Model. For the soft component due to the low energy cc-bar interactions with soft particles produced by other baryon-baryon collisions, the absorption cross sections are greater for ψ' than for J/ψ, because the breakup threshold for ψ' is much smaller than for ψ. (author)

[en] We explore molecular states of two open heavy-quark mesons (Qq)-(qQ) in a quark-based model in terms of a four-body nonrelativistic Hamiltonian with pairwise effective interactions. Molecular states are found in the combinations of {D,D*,B,B*} with {D,D*,B,B*}, including a weakly bound DD^* state near the threshold which may be qualitatively identified as the 3872 state observed recently by the Belle Collaboration

[en] We examine three different ways a heavy quarkonium can dissociate at high temperatures. The heavy quarkonium can dissociate spontaneously when it becomes unbound at a temperature above its dissociation temperature. Following the recent work of Digal, Petreczky, and Satz, we calculate the dissociation temperatures of heavy quarkonia taking into account the angular momentum selection rules and using a temperature-dependent potential inferred from lattice gauge calculations. We find that the selection rules change the dissociation temperatures substantially for charmonia but only slightly for bottomia. A quarkonium system in thermal equilibrium with the medium can dissociate by thermalization. The fraction of quarkonium lying above the dissociation threshold increases as temperature increases. A quarkonium can also dissociate by colliding with light hadrons. We evaluate the cross sections for the dissociation of J/ψ and Υ in collision with π as a function of the temperature of the hadron medium, using the quark-interchange model of Barnes and Swanson. We find that as the temperature increases, the threshold energy decreases and the dissociation cross section increases

[en] We follow and modify the Feshbach-Villars formalism by separating the Klein-Gordon equation into two coupled time-dependent Schroedinger equations for particle and antiparticle wave function components with positive probability densities. We find that the equation of motion for the probability densities is in the form of relativistic hydrodynamics where various forces have their classical counterparts, with the additional element of the quantum stress tensor that depends on the derivatives of the amplitude of the wave function. We derive the equation of motion for the Wigner function and we find that its approximate classical weak-field limit coincides with the equation of motion for the distribution function in the collisionless kinetic theory.