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Multiparticle Production in Strong Interactions

Söderberg, Fredrik LU (2003)
Abstract
An alternative formulation of the Lund fragmentation model for string states without gluons is presented. It is shown that the fragmentation process can be factorised into a product of transition operators with well-defined eigenfunctions and corresponding eigenvalues. The physical properties of these functions are studied and possible applications are suggested.



A fragmentation model for multigluon strings is defined and investigated in detail. The model fulfils the Lund area law on an event to event basis and it is formulated in a way which makes it suitable for a Monte Carlo implementation. A Monte Carlo fragmentation program, called ALFS, based upon this exact implementation of the Lund area law is analysed and... (More)
An alternative formulation of the Lund fragmentation model for string states without gluons is presented. It is shown that the fragmentation process can be factorised into a product of transition operators with well-defined eigenfunctions and corresponding eigenvalues. The physical properties of these functions are studied and possible applications are suggested.



A fragmentation model for multigluon strings is defined and investigated in detail. The model fulfils the Lund area law on an event to event basis and it is formulated in a way which makes it suitable for a Monte Carlo implementation. A Monte Carlo fragmentation program, called ALFS, based upon this exact implementation of the Lund area law is analysed and compared with the PYTHIA event generator. We find that inclusive distributions are the same but that there are differences on an event to event basis.



We demonstrate that the hadrons produced in this model can be grouped into (almost) planar regions in momentum space called Coherence Chains. A qualitative study of the properties of the Coherence Chains is performed using the above mentioned ALFS Monte Carlo fragmentation program. We find that the distribution in the number of hadrons in a Coherence Chain has stability properties which allows us to base a model for the Bose-Einstein effect upon the concept of Coherence Chains. The two particle correlation function for 2, 3 and 4 jet events is studied.



The thesis also contains a phenomenological investigation of a set of distributions obtained from the perturbative QCD parton cascades as they are implemented in the Monte Carlo event generators ARIADNE and PYTHIA. In an analysis built upon a generalised rapidity range, we observe a set of independent entities, that we call Generalised Dipoles. In the Lund model, the Generalised Dipoles correspond to connected plaquettes along a surface characteristic to the string state. We demonstrate that there is a close relationship between the Generalised Dipoles and the above mentioned Coherence Chains. (Less)
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author
opponent
  • Prof Csörgö, Tamas, H-1525 BudapestHUNGARY
organization
publishing date
type
Thesis
publication status
published
subject
keywords
Hadronisation, QCD, Bose-Einstein correlations, Elementary particle physics, Elementarpartikelfysik, quantum field theory, String fragmentation, kvantfältteori, Fysicumarkivet A:2003:Söderberg
pages
157 pages
publisher
Department of Theoretical Physics, Lund University
defense location
Lecture Hall F, Dept. of Theoretical Physics
defense date
2003-05-09 10:30
ISBN
91-628-5594-8
language
English
LU publication?
yes
id
0795c6d6-0a78-4bc4-937e-1c792110798e (old id 465715)
date added to LUP
2007-08-09 11:38:29
date last changed
2016-09-19 08:45:01
@phdthesis{0795c6d6-0a78-4bc4-937e-1c792110798e,
  abstract     = {An alternative formulation of the Lund fragmentation model for string states without gluons is presented. It is shown that the fragmentation process can be factorised into a product of transition operators with well-defined eigenfunctions and corresponding eigenvalues. The physical properties of these functions are studied and possible applications are suggested.<br/><br>
<br/><br>
A fragmentation model for multigluon strings is defined and investigated in detail. The model fulfils the Lund area law on an event to event basis and it is formulated in a way which makes it suitable for a Monte Carlo implementation. A Monte Carlo fragmentation program, called ALFS, based upon this exact implementation of the Lund area law is analysed and compared with the PYTHIA event generator. We find that inclusive distributions are the same but that there are differences on an event to event basis.<br/><br>
<br/><br>
We demonstrate that the hadrons produced in this model can be grouped into (almost) planar regions in momentum space called Coherence Chains. A qualitative study of the properties of the Coherence Chains is performed using the above mentioned ALFS Monte Carlo fragmentation program. We find that the distribution in the number of hadrons in a Coherence Chain has stability properties which allows us to base a model for the Bose-Einstein effect upon the concept of Coherence Chains. The two particle correlation function for 2, 3 and 4 jet events is studied.<br/><br>
<br/><br>
The thesis also contains a phenomenological investigation of a set of distributions obtained from the perturbative QCD parton cascades as they are implemented in the Monte Carlo event generators ARIADNE and PYTHIA. In an analysis built upon a generalised rapidity range, we observe a set of independent entities, that we call Generalised Dipoles. In the Lund model, the Generalised Dipoles correspond to connected plaquettes along a surface characteristic to the string state. We demonstrate that there is a close relationship between the Generalised Dipoles and the above mentioned Coherence Chains.},
  author       = {Söderberg, Fredrik},
  isbn         = {91-628-5594-8},
  keyword      = {Hadronisation,QCD,Bose-Einstein correlations,Elementary particle physics,Elementarpartikelfysik,quantum field theory,String fragmentation,kvantfältteori,Fysicumarkivet A:2003:Söderberg},
  language     = {eng},
  pages        = {157},
  publisher    = {Department of Theoretical Physics, Lund University},
  school       = {Lund University},
  title        = {Multiparticle Production in Strong Interactions},
  year         = {2003},
}