Baryon-number transfer in high-energy hp collisions

The processes of baryon-number transfer due to string-junction propagation in rapidity is considered. It has a significant effect on the net baryon production in pp collisions at mid-rapidities and an even larger effect in the forward hemisphere in the cases of πp and γp interactions. The results of numerical calculations in the framework of the quark-gluon string model are in reasonable agreement with the data with the same parameter values for different energies.     

Lorentz violation in high-energy ions

The theoretical interest in small Lorentz violations has motivated experiments that investigate it by measuring deviations in the time dilation predicted by special relativity (SR) using high-energy ions. The main contribution of this article is to show that including the Doppler effect in the emission (which is of the same order as the time dilation effect) in the analysis leads to differences between experimental and theoretical predictions that indicate potential Lorentz violation.     

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.     

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.     

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.     

Studying lepton family violation in lepton-lepton collisions

In the context of the future high energy – high luminosity electron and muon colliders, all the relevant four-lepton processes with the lepton family violation (LFV) are systematically classified. The most general LFV effective lagrangians are found, and the helicity differential cross sections for the LFV processes are calculated. The six- and eight-lepton Standard Model (SM) backgrounds are discussed, and the LFV processes clean of the six-lepton background are picked out. The possibility to suppress the six-lepton SM background, when present, by the unnatural initial beam polarizations is investigated. It is shown that the four-lepton LFV processes are amenable to experimental study in the lepton-lepton collisions in the most favourable cases up to the underlying scale of order TeV. Studying these processes should provide an essential part of the physics program for the next generation lepton colliders to unravel the outstanding flavour/family problem. Received: 20 October 1997 / Published online: 23 February 1998     

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.     

Quark mass differences in high-energy collisions

Assuming that the constituent quark masses are different, we investigate the effect that this will have on: (i) the asymmetric sharing of momentum between quarks in high-energy kaon and charmed particle interactions; (ii) the production of jets in e⁺e^?→hardrons; (iii) the impact parameter in kaon interactions.     

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.     

Clustering patterns in high-energy hadron collisions

The event-to-event fluctuations of the rapidity distributions are analyzed for semi-inclusive data obtained from 205 GeV/c and 303 GeV/c proton-proton collisions observed at NAL. The results indicate the presence of clustering effects, with cluster sizes approximating those observed in the quasi-elastic events. The average cluster size appears to be independent of the multiplicity of the final state.