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Parton Cascades and Hadronisation in High Energy Processes

Mohanty, Sandipan LU (2003)
Abstract (Swedish)
Popular Abstract in Swedish

Lunds strängfragmenteringsmodell beskriver hur färgade partiklar (kvarkar och gluoner, tillsammans kallade partoner) som produceras vid högenergetisk partikelkollisioner omvandlas till färgneutrala hadroner. Denna avhandling utvecklar och utforskar ett alternativt tillvägagångssätt till modellen. Den nya infallsvinkeln förbättrar modellen för system som består av många gluoner, samt system med liten invariant massa. Ett Monte Carlo program, ALFS, som implementerar modellen presenteras.



Hadroner i sluttillståndet kan enligt ALFS fördelas på en mängd kedjor benämnda <i>Koherenskedjor</i> med intresanta egenskaper. Antalet hadroner i en koherenskedja är endast svagt... (More)
Popular Abstract in Swedish

Lunds strängfragmenteringsmodell beskriver hur färgade partiklar (kvarkar och gluoner, tillsammans kallade partoner) som produceras vid högenergetisk partikelkollisioner omvandlas till färgneutrala hadroner. Denna avhandling utvecklar och utforskar ett alternativt tillvägagångssätt till modellen. Den nya infallsvinkeln förbättrar modellen för system som består av många gluoner, samt system med liten invariant massa. Ett Monte Carlo program, ALFS, som implementerar modellen presenteras.



Hadroner i sluttillståndet kan enligt ALFS fördelas på en mängd kedjor benämnda <i>Koherenskedjor</i> med intresanta egenskaper. Antalet hadroner i en koherenskedja är endast svagt beroende av kollisionens energi i tyngdpunktssystemet och av andra egenskaper karaktäristiska för händelsen. Dessa kedjors egenskaper kan spåras till egenskaper hos de <i>partonkaskader</i> som beskriver gluonstrålning, samt sönderfall av gluoner till kvark-antikvarkpar. Storleken av gluon-gluon-dipoler i dessa partonkaskader och besläktade strukturer, som benämns <i>generaliserade dipoler</i>, har många stabilitetsegenskaper som tyder på att de är huvudorsaker till ovan nämnda koherenskedjor.



Koherenskedjorna kan användas för att generalisera en tidigare undersökning av den så kallade Bose-Einstein effekten. Identiska bosoner som produceras vid en högenergetisk process brukar befinna sig lite närmare varandra i fasrummet jämfört med förutsägelser baserade på en semiklassisk beskrivning som Lundamodellen. Det är möjligt att införa effekten i Lundamodellen som en kvantmekanisk störningseffekt genom att lägga olika vikt på olika händelser. Tidigare undersökningar kunde inte hantera strängar med gluoner, vilket görs i denna avhandling. Dock är vår slutsats dagsläget, att denna analys är otillräcklig för att beskriva den experimentellt observerade signalen.



ALFS innehåller även en förbättrad hantering av det begränsade fasrummet tillgängligt för hadroner. Detta är mest relevant då strängen har liten invariant massa, så att bara några få hadroner produceras. Det är dock väntat, att den nya hanteringen av fasrummet påverkar korrelationer mellan partiklar även för större invarianta massor. (Less)
Abstract
The Lund string fagmentation model was reformulated as a process along the boundary curve of the string called the directrix, in order to treat multigluon strings according to the Lund model area law. It was found that the hadrons in the final state could be collected into several groups, in such a way that the energy-momenta of the hadrons in a group lie in a plane in the Minkowski space within small transverse fluctuations. The origin of these structures, named Coherence Chains, was traced to properties of gluon radiation in coherent parton cascades. The distribution of the size of gluon-gluon dipoles was found to be stable against changes in the global event properties as well as changes in the resolution scale, when the size was... (More)
The Lund string fagmentation model was reformulated as a process along the boundary curve of the string called the directrix, in order to treat multigluon strings according to the Lund model area law. It was found that the hadrons in the final state could be collected into several groups, in such a way that the energy-momenta of the hadrons in a group lie in a plane in the Minkowski space within small transverse fluctuations. The origin of these structures, named Coherence Chains, was traced to properties of gluon radiation in coherent parton cascades. The distribution of the size of gluon-gluon dipoles was found to be stable against changes in the global event properties as well as changes in the resolution scale, when the size was defined relative to the resolution scale. These properties were explained as consequences of a balance between increased probability for gluon emission because of the running coupling constant in QCD, which results in a decrease of the size of individual dipoles, and a compensating increase of the size measure, owing to the smaller resolution scale. These properties of the colour dipoles translated into stability properties of certain more abstract entities which are relevant to the new approach to string fragmentation. These were named Generalised Dipoles and they were identified as the chief contributing factors for similar properties of the coherence chains. The proporties of the coherence chains were used to extend an interference based model for Bose-Einstein correlations into a model applicable to multigluon strings. The extended model was used to investigate the two particle correlation function for identical pions in multijet events. The hadronisation model was further developed to include effects of limitted available phase space for hadron formation in systems with small invariant mass. (Less)
Please use this url to cite or link to this publication:
author
opponent
  • Prof Białas, Andrzej, Institute of Physics. Jagiellonian University. Kraków Poland
organization
publishing date
type
Thesis
publication status
published
subject
keywords
small invariant mass hadronic systems, hadronisation, parton cascades, Elementary particle physics, Elementarpartikelfysik, kvantfältteori, quantum field theory, Bose-Einstein correlations, Fysicumarkivet A:2003:Mohanty
pages
161 pages
publisher
Department of Theoretical Physics, Lund University
defense location
Lecture Hall F, Department of Theoretical Physics
defense date
2003-05-16 10:30
ISBN
ISBN 91-628-5606-5
language
English
LU publication?
yes
id
dc45c418-981a-4548-81eb-69fa1eea0fa7 (old id 465731)
date added to LUP
2007-08-09 11:01:23
date last changed
2016-09-19 08:45:13
@misc{dc45c418-981a-4548-81eb-69fa1eea0fa7,
  abstract     = {The Lund string fagmentation model was reformulated as a process along the boundary curve of the string called the directrix, in order to treat multigluon strings according to the Lund model area law. It was found that the hadrons in the final state could be collected into several groups, in such a way that the energy-momenta of the hadrons in a group lie in a plane in the Minkowski space within small transverse fluctuations. The origin of these structures, named Coherence Chains, was traced to properties of gluon radiation in coherent parton cascades. The distribution of the size of gluon-gluon dipoles was found to be stable against changes in the global event properties as well as changes in the resolution scale, when the size was defined relative to the resolution scale. These properties were explained as consequences of a balance between increased probability for gluon emission because of the running coupling constant in QCD, which results in a decrease of the size of individual dipoles, and a compensating increase of the size measure, owing to the smaller resolution scale. These properties of the colour dipoles translated into stability properties of certain more abstract entities which are relevant to the new approach to string fragmentation. These were named Generalised Dipoles and they were identified as the chief contributing factors for similar properties of the coherence chains. The proporties of the coherence chains were used to extend an interference based model for Bose-Einstein correlations into a model applicable to multigluon strings. The extended model was used to investigate the two particle correlation function for identical pions in multijet events. The hadronisation model was further developed to include effects of limitted available phase space for hadron formation in systems with small invariant mass.},
  author       = {Mohanty, Sandipan},
  isbn         = {ISBN 91-628-5606-5},
  keyword      = {small invariant mass hadronic systems,hadronisation,parton cascades,Elementary particle physics,Elementarpartikelfysik,kvantfältteori,quantum field theory,Bose-Einstein correlations,Fysicumarkivet A:2003:Mohanty},
  language     = {eng},
  pages        = {161},
  publisher    = {ARRAY(0xb4a0650)},
  title        = {Parton Cascades and Hadronisation in High Energy Processes},
  year         = {2003},
}