Non-extensive statistics, fluctuations and correlations in high-energy nuclear collisions

Starting from the experimental evidence that high-energy nucleus–nucleus collisions cannot be described in terms of superpositions of elementary nucleon–nucleon interactions, we analyze the possibility that memory effects and long-range forces imply a non-extensive statistical regime during high-energy heavy-ion collisions. The relevance of these statistical effects and their compatibility with the available experimental data are discussed. In particular, we show that theoretical estimates obtained in the framework of the generalized non-extensive thermostatistics, can reproduce the shape of the pion transverse mass spectrum and explain the different physical origin of the transverse momentum correlation function of the pions emitted during the central Pb + Pb and during the p +p collisions at 158 GeV. Received: 6 June 1999 / Published online: 21 December 1999     

Mass yield in high-energy proton-uranium collisions from a complete,microcanonical statistical decay

The properties of charge exchange reactions induced by¹³C projectiles of 30 MeV/u are discussed. Spectra on¹²C as target have been measured and are used to illustrate the properties of the (¹³C,¹³N) and (¹³C,¹³B) reactions. Both reactions show selective population of states, the (¹³C,¹³B) reactions favours the spin-flip (Δs=1) transitions.The Giant Dipole Resonance is strongly excited in both reactions.     

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.     

Non-extensive statistical entropy,quantum groups and quantum entanglement

In this work, we explore a new connection between quantum groups and Tsallis entropy through the energy spectrum of a Hamiltonian with S_Uq(2)$S{U}_q\left(2\right)$ symmetry. Identifying the deformation parameter of the entropy with the parameter of deformation of the associated quantum group, we deduce Tsallis entropy for states related to such a system with S_Uq(2)$S{U}_q\left(2\right)$ symmetry and conducted an investigation of quantum entanglement.     

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.     

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.     

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.     

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.     

Partonic collectivity in high-energy nuclear collisions

We show evidences for partonic flow in Au+Au collisions at RHIC.     

Quark production in high-energy proton-nucleus collisions

In this note, we discuss the problem of quark-antiquark pair production in the framework of the color glass condensate. The cross-section can be calculated in closed form for the case of proton-nucleus collisions, where the proton can be considered to be a dilute object. We find that -factorization is broken by rescattering effects.Arrival of the final proofs: 4 May 2005PACS: 11.80.La, 11.15.Kc     

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.