Showing papers by "Arnaud Ferrari published in 1996"

Cascade particles, nuclear evaporation, and residual nuclei in high energy hadron-nucleus interactions

Abstract: Based on a Monte Carlo realization of the Dual Parton Model we study the production of target associated particles and of nuclear fragments in high energy hadronnucleus interactions. A formation zone intranuclear cascade of low energy secondaries inside the target nucleus is discussed. We calculate excitation energies of residual nuclei left after the intranuclear cascade process and treat their further disintegration by introducing models for the evaporation of protons, neutrons, and light fragments, high energy fission, and by applying a Fermi Break-up model to light nuclear fragments. The results are compared to data on target associated particle production. We furthermore calculate cross sections for the production of nuclear fragments.

The production of residual nuclei in peripheral high energy nucleus-nucleus interactions

Abstract: A formation zone intranuclear cascade model is applied to peripheral nucleus-nucleus collisions. We calculate the excitation energies of prefragments, treat their further nuclear disintegration and introduce a model for nuclear deexcitation by photon emission. Results are compared to data on target associated particle production in nucleus-nucleus collisions. We discuss implications of these models to the description of particle production in the fragmentation regions. Special emphasis is put on applications for air showers induced by cosmic ray nuclei and for residual nucleus production at heavy ion colliders.

Phenomenology and Modelling of Large-Scale Jets

Abstract: Supersonic jets ejected from Active Galactic Nuclei were proposed 20 years ago to explain extended radio galaxies. Today that proposal has been verified by many high angular resolution observations at radio and optical frequencies and by indirect data at X and γ rays. The interpretation of these objects requires investigations of nonlinear fluid phenomena to interpret the origin, propagation and termination of collimated outflows and their nonthermal emissivity. On the other hand the observed phenomenology requires to follow the time evolution of the relevant physical processes in physical conditions that cannot be reproduced in laboratory experiments. in these lectures a review of recent investigations on jets is presented, the results are compared with observational data and directions for future studies are indicated.

Supersonic Jets and Lobe Morphologies

Abstract: Since the pioneering work by Norman et al. (1982), many numerical studies have been devoted to the analysis of the propagation of a supersonic jet shot into an ambient medium (see Massaglia, Bodo & Ferrari 1995, hereinafter Paper I, and references therein). In spite of these strong efforts many aspects of this problem are still not well understood. This is due to the complexity of the jet-cocoon structure: in fact, the cocoon excites perturbations to the jet flow, which in turn can be amplified by the Kelvin-Helmholtz mechanism and induce a strong activity of the jet’s head that affects the cocoon structure. Thus a complex feedback loop mechanism establishes between jet and cocoon which make the dynamics of the interaction very complex.

Fractal Properties of Extragalactic Jets: Evidence of Turbulence?

Abstract: Several different properties of extragalactic radio sources have been attributed to the effects of turbulence. The morphological appearance of FRI sources has been often interpreted as the result of turbulent entrainment in subsonic or transonic flows (Bicknell 1984, 1986). Moreover, particle acceleration by MHD turbulence via a second order Fermi process is one of the possible ways for accelerating the synchrotron emitting relativistic particles (see Ferrari, Trussoni & Zaninetti 1979). Turbulence appears therefore as an important ingredient in the theoretical modelling of extragalactic radio sources; however, we do not have, unfortunately, any direct evidence of it.

MHD Equilibria of Helical Jets

Abstract: From recent high angular resolution (~ 0.l arcsec) observations of some extragalactic jets (in particular we refer to the radio, optical, and ultraviolet images of the M 87 jet, of 3C 66B, and 3C 264) it can be inferred that the synchrotron emission from the jet comes mainly from an external, quasicylindrical surface on which bright helical filamentary structures can be clearly recognized.

The production of residual nuclei in peripheral high energy nucleus-nucleus interactions

Abstract: A formation zone intranuclear cascade model is applied to peripheral nucleus-nucleus collisions. We calculate the excitation energies of prefragments, treat their further nuclear disintegration and introduce a model for nuclear deexcitation by photon emission. Results are compared to data on target associated particle production in nucleus-nucleus collisions. We discuss implications of these models to the description of particle production in the fragmentation regions. Special emphasis is put on applications for air showers induced by cosmic ray nuclei and for residual nucleus production at heavy ion colliders.