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Soft color interactions and diffractive hard scattering at the Fermilab Tevatron
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Nuclear and Particle Physics, High Energy Physics. (THEORETICAL HIGH ENERGY PHYSICS)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Nuclear and Particle Physics, High Energy Physics. (THEORETICAL HIGH ENERGY PHYSICS)
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Nuclear and Particle Physics, High Energy Physics.
2001 (English)In: Physical Review D, ISSN 1550-7998, Vol. 64, no 11, 114015- p.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.

Place, publisher, year, edition, pages
2001. Vol. 64, no 11, 114015- p.
National Category
Physical Sciences
Identifiers
URN: urn:nbn:se:uu:diva-90287DOI: 10.1103/PhysRevD.64.114015OAI: oai:DiVA.org:uu-90287DiVA: diva2:162591
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2012-03-12Bibliographically approved
In thesis
1. Quantum chromodynamics and colour singlet exchange in high energy interactions
Open this publication in new window or tab >>Quantum chromodynamics and colour singlet exchange in high energy interactions
2003 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Quantum chromodynamics (QCD) is the fundamental theory in elementary particle physics that describes the strong interaction in terms of exchanges of force-carrying, colour-charged particles known as gluons. Although well-established through experimental verifications, there are fundamental unsolved problems in the theory.

In this thesis, some novel aspects of strong interaction dynamics are studied in the context of colour singlet exchange processes — interactions where complex systems of gluons with no net colour charge are exchanged. Both perturbative and non-perturbative QCD methods are used, as well as Monte Carlo computer simulations.

Soft colour interactions in the final state of a high energy collision can lead to effective colour singlet exchange. Non-perturbative models for such interactions are shown to give a good description of diffractive production of W, Z, bb, J/ψ and jets in pp collisions at the Tevatron. Predictions are given for diffractive Higgs boson and prompt photon production at hadron colliders.

Rapidity gaps between jets is a new phenomenon which is studied with an improved perturbative calculation of hard colour singlet exchange using the BFKL equation, taking into account previously neglected contributions and non-leading logarithmic corrections. Including also underlying soft rescattering effects, the complete model reproduces well data from the Tevatron.

Diffractive vector meson production through hard colour singlet exchange in γp collisions is studied in the framework of the conformal invariant non-forward solution of the BFKL equation. Expressions for helicity-dependent amplitudes are derived, and the results show good agreement with data on J/ψ and ρ production from the ep collider HERA.

These studies lead to a deeper knowledge of complex gluon dynamics, and therefore advance our understanding of QCD.

Abstract [sv]

X

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2003. 75 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 829
Keyword
Physics, Fysik
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-3385 (URN)91-554-5598-0 (ISBN)
Public defence
2003-05-16, the Polhem lecture hall (10134), Ångström laboratory, Uppsala, 10:15
Opponent
Supervisors
Available from: 2003-04-15 Created: 2003-04-15 Last updated: 2012-03-12Bibliographically approved
2. The colour of gluon interactions: Studies of Quantum Chromodynamics in soft and hard processes
Open this publication in new window or tab >>The colour of gluon interactions: Studies of Quantum Chromodynamics in soft and hard processes
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. 64 p.
Series
Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1104-232X ; 774
Keyword
Physics, Fysik
National Category
Physical Sciences
Research subject
Physics
Identifiers
urn:nbn:se:uu:diva-2850 (URN)91-554-5464-X (ISBN)
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

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Enberg, RikardIngelman, GunnarTimneanu, Nicusor

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