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The colour of gluon interactions: Studies of Quantum Chromodynamics in soft and hard processes
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Nuclear and Particle Physics, High Energy Physics.
2002 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantum Chromodynamics (QCD) is the theory of the strong interaction, one of the fundamental forces of nature. The interactions between quarks are mediated by gluons, which are the colour-charged gauge fields in QCD. Hard processes with a large momentum transfer can be calculated using perturbation theory, while soft processes with a small momentum transfer are poorly understood. In this thesis, various aspects of the gluon interactions are studied based on the interplay between hard and soft processes.

Soft gluon exchanges do not affect the dynamics of a hard process, but can rearrange the colour topology, resulting in different final states. The soft colour interaction models employ this idea and give a good description of all diffractive hard scattering data observed in pp collisions (W, Z, dijets, bb, J/ψ). This thesis also presents predictions for diffractive Higgs and γγ production at present and future hadron colliders.

Multiple gluon exchanges give rise to saturation effects in hadronic collisions at high energies. Implementing this idea in photon-photon collisions gives new insight into the quantum structure of the photon and its interactions at high energies. When combined with perturbative calculations for single gluon exchange, the obtained results are in good agreement with experimental data from e+e- colliders.

Off-shell gluon distributions in the photon give another perspective on the photon structure and have been parameterized for the first time in this thesis. These are useful for calculating cross sections of processes where the effects of transverse momenta are crucial, for example heavy quark production in γp or γγ collisions.

Quantization of gauge fields which have a richer gauge structure than the gluons in QCD, is studied using the powerful BRST quantization formalism. Thus, first-stage reducible theories, like topological Yang-Mills and spin-5/2 gauge fields, are successfully quantized in an irreducible way.

Understanding gluon interactions and the interplay between soft and hard processes paves the way towards solving the longstanding problem of confinement in QCD.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis , 2002. , p. 64
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 774
Keywords [en]
Physics
Keywords [sv]
Fysik
National Category
Physical Sciences
Research subject
Physics
Identifiers
URN: urn:nbn:se:uu:diva-2850ISBN: 91-554-5464-X (print)OAI: oai:DiVA.org:uu-2850DiVA, id: diva2:162120
Public defence
2002-12-12, the Polhem lecture hall (10134) at the Ångström laboratory, Uppsala, 10:15
Opponent
Available from: 2002-11-21 Created: 2002-11-21 Last updated: 2012-10-10Bibliographically approved
List of papers
1. Soft remnant interactions and rapidity gaps
Open this publication in new window or tab >>Soft remnant interactions and rapidity gaps
2000 (English)Conference paper, Published paper (Other scientific)
Abstract [en]

Soft colour exchange models give a unified description of both diffractive and non-diffractive events, such that e-p and p-pbar collider data with and without rapidity gaps are well reproduced. We show that these models also describe the new Tevatron data

National Category
Other Physics Topics
Identifiers
urn:nbn:se:uu:diva-35001 (URN)
Available from: 2008-06-10 Created: 2008-06-10 Last updated: 2012-03-12
2. Soft color interactions and diffractive hard scattering at the Fermilab Tevatron
Open this publication in new window or tab >>Soft color interactions and diffractive hard scattering at the Fermilab Tevatron
2001 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 64, no 11, p. 114015-Article in journal (Refereed) Published
Abstract [en]

An improved understanding of nonperturbative QCD can be obtained by the recently developed soft color interaction models. Their essence is the variation of color string-field topologies, giving a unified description of final states in high energy interactions, e.g., diffractive and nondiffractive events in ep and pp̅ . Here we present a detailed study of such models (the soft color interaction model and the generalized area law model) applied to pp̅ , considering also the general problem of the underlying event including beam particle remnants. With models tuned to DESY HERA ep data, we find a good description also of Fermilab Tevatron data on production of W, beauty and jets in diffractive events defined either by leading antiprotons or by one or two rapidity gaps in the forward or backward regions. We also give predictions for diffractive J/ψ production where the soft exchange mechanism produces both a gap and a color singlet cc̅ state in the same event. This soft color interaction approach is also compared with Pomeron-based models for diffraction, and some possibilities to experimentally discriminate between these different approaches are discussed.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-90287 (URN)10.1103/PhysRevD.64.114015 (DOI)
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2017-12-14Bibliographically approved
3. Diffractive Higgs Boson Production at the Fermilab Tevatron and the CERN Large Hadron Collider
Open this publication in new window or tab >>Diffractive Higgs Boson Production at the Fermilab Tevatron and the CERN Large Hadron Collider
2002 (English)In: Physical Review Letters, ISSN 0031-9007, E-ISSN 1079-7114, Vol. 89, no 8, p. 081801-Article in journal (Refereed) Published
Abstract [en]

Improved possibilities to find the Higgs boson in diffractive events, having less hadronic activity, depend on whether the cross section is large enough. Based on the soft color interaction models that successfully describe diffractive hard scattering at DESY HERA and the Fermilab Tevatron, we find that only a few diffractive Higgs events may be produced at the Tevatron, but we predict a substantial rate at the CERN Large Hadron Collider.

National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-90288 (URN)10.1103/PhysRevLett.89.081801 (DOI)
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2017-12-14Bibliographically approved
4. Diffractive Higgs Production: Soft Colour Interactions Perspective
Open this publication in new window or tab >>Diffractive Higgs Production: Soft Colour Interactions Perspective
2002 (English)In: Acta Physica Polonica B, ISSN 0587-4254, E-ISSN 1509-5770, Vol. B33, no 11, p. 3479-Article in journal, Meeting abstract (Refereed) Published
Abstract [en]

We briefly present the soft colour interaction models which are successful in reproducing a multitude of diffractive hard scattering data, and give predictions for diffractive Higgs production at the Tevatron and LHC. Only a few diffractive Higgs events may be produced at the Tevatron, but we predict a substantial rate at the LHC.

Place, publisher, year, edition, pages
Jagellonian University, Cracow, 2002
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-45272 (URN)
Conference
The X International Workshop on Deep Inelastic Scattering (DIS2002), 30 April - 4 May 2002, Cracow
Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2017-12-05Bibliographically approved
5. Diffractive Higgs bosons and prompt photons at hadron colliders
Open this publication in new window or tab >>Diffractive Higgs bosons and prompt photons at hadron colliders
2003 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 67, p. 011301-Article in journal (Refereed) Published
Abstract [en]

Models for soft color interactions have been successful in describing and predicting diffractive hard scattering processes in ep collisions at DESY HERA and pp̅ at the Fermilab Tevatron. Here we present new comparisons of the model to recent diffractive dijet data, also showing good agreement. The topical issue of diffractive Higgs boson production at the Tevatron and CERN LHC hadron colliders is further investigated. For H⃗γγ the irreducible background of prompt photon pairs from qq̅ →γγ and gg⃗γγ is always dominating, implying that higher branching ratio decay modes of the Higgs boson have to be used. However, such prompt photons can be used to test the basic prediction for Higgs boson production since gg⃗γγ involves a quark loop diagram similar to gg⃗H.

National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-90289 (URN)10.1103/PhysRevD.67.011301 (DOI)
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2017-12-14Bibliographically approved
6. Saturation model for two-photon interactions at high energies
Open this publication in new window or tab >>Saturation model for two-photon interactions at high energies
2002 (English)In: European Physical Journal C, ISSN 1434-6044, E-ISSN 1434-6052, Vol. 23, no 3, p. 513-526Article in journal (Refereed) Published
Abstract [en]

We formulate and analyse a saturation model for the total γγ and γ∗γ∗ cross-sections and for the real photon structure function Fγ2(x,Q2) . The model is based on a picture in which the γ∗γ∗ total cross-section for arbitrary photon virtualities is driven by the interaction of colour dipoles into which the virtual photons fluctuate. The cross-section describing this interaction is assumed to satisfy the saturation property with the saturation radius taken from the Golec-Biernat and Wüsthoff analysis of the γ∗p interaction at HERA. The model is supplemented by the QPM and non-pomeron reggeon contributions. The model gives a very good description of the data on the γγ total cross-section, on the photon structure function Fγ2(x,Q2) at lowx and on the γ∗γ∗ cross-section extracted from LEP double tagged events. The production of heavy flavours in γγ collisions is also studied. Predictions of the model for the very high energy range which will be probed at future linear colliders are given.

Place, publisher, year, edition, pages
Springer-Verlag, Berlin, Heidelberg, 2002
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-45293 (URN)10.1007/s100520200893 (DOI)
Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2017-12-05Bibliographically approved
7. Saturation model for 2-gamma physics
Open this publication in new window or tab >>Saturation model for 2-gamma physics
2002 (English)In: Acta Physica Polonica B, ISSN 0587-4254, E-ISSN 1509-5770, Vol. B33, no 10, p. 3045-3050Article in journal, Meeting abstract (Refereed) Published
Abstract [en]

We introduce a saturation model for photon-photon interactions, based on a QCD dipole picture of high energy scattering. The two-dipole cross-section is assumed to satisfy the saturation property. This pomeron-like contribution is supplemented with QPM and non-pomeron reggeon contributions. The model gives a very good description of the data on the \gamma \gamma total cross-section, on the photon structure function F2\gamma (x,Q2) at low x and on the \gamma * \gamma * cross section.

Place, publisher, year, edition, pages
Jagellonian University, Cracow, 2002
National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-45274 (URN)
Conference
The X International Workshop on Deep Inelastic Scattering (DIS2002), 30 April - 4 May 2002, Cracow
Available from: 2008-10-17 Created: 2008-10-17 Last updated: 2017-12-05Bibliographically approved
8. Unintegrated gluon in the photon and heavy quark production
Open this publication in new window or tab >>Unintegrated gluon in the photon and heavy quark production
2003 (English)In: European Physical Journal C, Vol. 27, p. 73-85Article in journal (Refereed) Published
Abstract [en]

The unintegrated gluon density in the photon is determined, using the Kimber-Martin-Ryskin prescription. In addition, a model of the unintegrated gluon is proposed, based on the saturation model extended to the large-x region. These gluon densities are ap

Identifiers
urn:nbn:se:uu:diva-45277 (URN)
Available from: 2007-03-21 Created: 2007-03-21 Last updated: 2012-03-12

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