A model for high-energy heavy-ion collisions

A model is developed for high-energy heavy-ion collisions that treats the variation across the overlap region of the target and projectile in the amount of energy and momentum that is deposited. The expression for calculating any observable takes the form of a sum over a series of terms, each one of which consists of a geometric, a kinematic, and a statistical factor. The geometrical factors for a number of target projectile systems are tabulated.     

A one-dimensional model of associated production in high-energy hadron collisions

We estimate production processes in the one-dimensional approximation of the dual unitary approach to hadron collisions. Strange particle production is in satisfactory agreement with estimates from data; charmed particle production is found to be observably large.     

Three-step analytic model for high-energy heavy-ion collisions

We discuss within the framework of an analytical model central collisions between large nuclei at an intermediate energy. The model assumes three stages: the ignition stage in which thermalized nucleons are created within the reaction volume; the expansion phase in which the hot nuclear matter expands and cools; and finally, the evaporation stage in which the system disintegrates through a surface evaporation. The model provides a qualitative insight into the connections between the main physical processes throughout the collision event.     

Multiparton collisions and multiplicity distribution in high-energy collisions

We discuss the multiplicity distribution for the highest accessible energies of pp- and -interactions from the point of view of multiparton collisions. The inelastic cross sections for single, σ₁, and multiple (double and, presumably, triple), σ₂ parton collisions are calculated from the analysis of experimental data on the multiplicity distribution up to Tevatron energies. It is found that σ₁ becomes energy independent while σ₂ increases with for GeV. The observed growth of p with multiplicity is attributed to the increasing role of multiparton collisions for the high-energy -inelastic interactions. σ₂₊₃ reproduces quite well the cross-section for the mini-jet production.     

Dileptons in high-energy heavy-ion collisions

The current status of our understanding of dilepton production in ultra-relativistic heavyion collisions is discussed with special emphasis on signals from the (approach towards) chirally restored and deconfined phases. In particular, recent results of the CERN-SPS low-energy runs are compared to model predictions and interpreted. Prospects for RHIC experiments are given.     

CP-tests in high-energy proton-antiproton collisions

A general analysis of CP-violating correlations forW,Z and jet production in proton-antiproton collisions is presented. We consider unpolarizedp, beams, but a polarisation analysis of the producedW's andZ's. New CP-violating interactions beyond the standard model are parametrized by an effective Lagrangian. The bounds obtainable on the parameters of this Lagrangian from measurements are discussed. Finally we point out that a particular combination of polarisation observables of theW's and theZ allows a direct determination of the gluon distribution in the proton if the quark distributions are assumed to be known.     

Analytical treatment of high-energy nucleus-nucleus collisions

We review an analytical study of high-energy nucleus-nucleus collisions based on Boltzmann's kinetic theory of gases. In the first part of the paper, we do not take effects of the nuclear mean field into account. This turns out to be appropriate for particle inclusive production, as the good agreement of the theory with a large variety of inclusive experimental data demonstrates. As soon as physical observables extracted from measurements on an event per event basis are considered, the nuclear potential plays a decisive rôle. To account for this fact, we extend the theory by including the nuclear mean field in the Boltzmann equation. The results obtained are in qualitative agreement with experimental exclusive observables such as the sideward kinetic energy flow angle and the average transverse momentum, despite the absence of strong compression of nuclear matter in the theory presented.     

A proposed analysis of multiplicity fluctuations in high-energy heavy-ion collisions

A procedure for analyzing the data on multiplicity distributions in ultra-relativistic nucleus-nucleus collisions is proposed. A specific plot of the dispersion versus rapidity window is suggested so that significant information on dynamical fluctuation can be extracted. Arguments are presented to advance the speculation that the proposed analysis may be a method to discover signatures of quark-gluon plasma.     

Thermal dileptons in high-energy nuclear collisions

Clear signs of excess dileptons above the known sources have been found at the SPS for a long time. However, a real clarification of these observations was only recently achieved by NA60, measuring dimuons with unprecedented precision in 158A GeV In-In collisions. The excess mass spectrum in the region is consistent with a dominant contribution from π⁺π⁻→ρ→μ⁺μ⁻ annihilation. The associated ρ spectral function shows a strong broadening, but essentially no shift in mass. In the region , the excess is found to be prompt, not due to enhanced charm production. The inverse slope parameter associated with the transverse momentum spectra rises with mass up to the ρ, followed by a sudden decline above. While the initial rise, coupled to a hierarchy in hadron freeze-out, points to radial flow of a hadronic decay source, the decline above signals a transition to a low-flow source, presumably of partonic origin. The mass spectra show a steep rise towards low masses characteristic of Planck-like radiation. The polarization of the excess referred to the Collins Soper frame is found to be isotropic. All observations are consistent with a global interpretation of the excess as thermal radiation. We conclude with a short discussion of a possible link to direct photons.     

Electron capture in high-energy ion-atom collisions

We discuss the non-relativistic theory of electron capture from atoms (or ions) by ions when the relative velocity of the collision is greater than the orbital velocity of the captured electron. We emphasize the specific difficulties due to the two-body Coulomb potentials occurring in this process We show how the simplifications introduced by the small value of the electron to proton mass ratio can be used to provide a valuable tool to evaluate the adequacy of the existing theories. Extensive comparisons between theory and experiment are carried out and a number of new theoretical results are presented.     

Muon-electron events in high-energy proton-proton collisions

The tube models of nuclear production are questioned by pointing out that they cannot explain the dependence of the inclusive rapidity distribution width and the two-particle correlation function on the atomic number of the target nucleus.