Advanced

Statistical and Dynamical Aspects of Intermediate Energy Nuclear Collisions

Ghetti, Roberta LU (1997) In Cosmic and Subatomic Physics Dissertation
Abstract
Studies of intermediate energy heavy ion reactions have revealed the existence of a number of reducibility and thermal scaling properties in nuclear multifragmentation. In particular, the probability of emitting n-fragments is reducible to the probability of emitting a single fragment through the binomial distribution. The resulting one-fragment probability shows a dependence on the thermal energy that is characteristic of statistical decay. Similarly, the charge distributions associated with n-fragment emission are reducible to the one-fragment charge distribution, and thermal scaling is observed. Binomial and Poisson simulations of multifragment decay confirm the above experimental findings.



The reducibility equation... (More)
Studies of intermediate energy heavy ion reactions have revealed the existence of a number of reducibility and thermal scaling properties in nuclear multifragmentation. In particular, the probability of emitting n-fragments is reducible to the probability of emitting a single fragment through the binomial distribution. The resulting one-fragment probability shows a dependence on the thermal energy that is characteristic of statistical decay. Similarly, the charge distributions associated with n-fragment emission are reducible to the one-fragment charge distribution, and thermal scaling is observed. Binomial and Poisson simulations of multifragment decay confirm the above experimental findings.



The reducibility equation for the n-fragment charge distributions contains a quantity with a value that starts from zero, at low transverse energies, and saturates at high transverse energies. This evolution may signal a transition from a coexistence phase to a vapor phase. In the search for a signal of liquid-gas phase transition, the appearance of intermittency is reconsidered. Percolation calculations, as well as data analysis, indicate that an intermittent-like signal appears from classes of events that do not coincide with the critical one.



Information about the dynamical evolution of nuclear sources formed in intermediate energy heavy ion collisions can be gained by means of intensity interferometry. In particular, simultaneous neutron-neutron, proton-neutron and proton-proton interferometry measurements are interesting, since different effects participate differently in the correlations between different types of particle pairs. The simultaneous measurement of particles with nearly equal momenta is a very delicate experimental task, and in particular two-neutron interferometry is plagued by instrumental problems, such as low detection efficiency, background noise and neutron rescattering between detectors (cross-talk). The strength of the measured correlation functions is found to depend on the energy of the particle pair. The measured proton-neutron correlation function shows less strength than expected, possibly due to the Coulomb interaction of the proton with the emitting source.



The dynamical aspects of nuclear collisions can be probed by studying meson production. Complete pion production excitation functions can be measured in ramped-beam experiments at storage rings. In such experiments, particular attention must be payed to the delicate problem of translating the measured yields into absolute cross sections. Information on the pion production mechanism can be obtained by comparison of the measured yields with predictions from different model calculations. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof Braun-Munzinger, Peter, GSI Darmstadt, Germany
organization
publishing date
type
Thesis
publication status
published
subject
keywords
excitation function., subthreshold pions, pion production, neutron cross-talk, correlation function, interferometry, intermittency, phase transition, thermal scaling, reducibility, multifragmentation, Heavy ion collisions, intermediate energy, Atomic and molecular physics, Atom- och molekylärfysik
in
Cosmic and Subatomic Physics Dissertation
pages
184 pages
publisher
Experimental High-Energy Physics
defense location
Department of Physics (Sal B)
defense date
1997-02-28 10:15
external identifiers
  • other:ISRN: LUNFD6/NFFK-1012-SE+184P
ISSN
1101-4202
ISBN
91-973077-0-X
language
English
LU publication?
yes
id
6ac64d20-76a8-4fed-9356-c2d02be0b0c6 (old id 29024)
date added to LUP
2007-06-12 13:35:06
date last changed
2016-09-19 08:44:54
@phdthesis{6ac64d20-76a8-4fed-9356-c2d02be0b0c6,
  abstract     = {Studies of intermediate energy heavy ion reactions have revealed the existence of a number of reducibility and thermal scaling properties in nuclear multifragmentation. In particular, the probability of emitting n-fragments is reducible to the probability of emitting a single fragment through the binomial distribution. The resulting one-fragment probability shows a dependence on the thermal energy that is characteristic of statistical decay. Similarly, the charge distributions associated with n-fragment emission are reducible to the one-fragment charge distribution, and thermal scaling is observed. Binomial and Poisson simulations of multifragment decay confirm the above experimental findings.<br/><br>
<br/><br>
The reducibility equation for the n-fragment charge distributions contains a quantity with a value that starts from zero, at low transverse energies, and saturates at high transverse energies. This evolution may signal a transition from a coexistence phase to a vapor phase. In the search for a signal of liquid-gas phase transition, the appearance of intermittency is reconsidered. Percolation calculations, as well as data analysis, indicate that an intermittent-like signal appears from classes of events that do not coincide with the critical one.<br/><br>
<br/><br>
Information about the dynamical evolution of nuclear sources formed in intermediate energy heavy ion collisions can be gained by means of intensity interferometry. In particular, simultaneous neutron-neutron, proton-neutron and proton-proton interferometry measurements are interesting, since different effects participate differently in the correlations between different types of particle pairs. The simultaneous measurement of particles with nearly equal momenta is a very delicate experimental task, and in particular two-neutron interferometry is plagued by instrumental problems, such as low detection efficiency, background noise and neutron rescattering between detectors (cross-talk). The strength of the measured correlation functions is found to depend on the energy of the particle pair. The measured proton-neutron correlation function shows less strength than expected, possibly due to the Coulomb interaction of the proton with the emitting source.<br/><br>
<br/><br>
The dynamical aspects of nuclear collisions can be probed by studying meson production. Complete pion production excitation functions can be measured in ramped-beam experiments at storage rings. In such experiments, particular attention must be payed to the delicate problem of translating the measured yields into absolute cross sections. Information on the pion production mechanism can be obtained by comparison of the measured yields with predictions from different model calculations.},
  author       = {Ghetti, Roberta},
  isbn         = {91-973077-0-X},
  issn         = {1101-4202},
  keyword      = {excitation function.,subthreshold pions,pion production,neutron cross-talk,correlation function,interferometry,intermittency,phase transition,thermal scaling,reducibility,multifragmentation,Heavy ion collisions,intermediate energy,Atomic and molecular physics,Atom- och molekylärfysik},
  language     = {eng},
  pages        = {184},
  publisher    = {Experimental High-Energy Physics},
  school       = {Lund University},
  series       = {Cosmic and Subatomic Physics Dissertation},
  title        = {Statistical and Dynamical Aspects of Intermediate Energy Nuclear Collisions},
  year         = {1997},
}