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Dynamic colour screening in diffractive deep inelastic scattering
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
2016 (English)In: PHYSICAL REVIEW D, ISSN 2470-0010, Vol. 93, no 9, 094016Article in journal (Other academic) Published
Abstract [en]

We present a novel Monte Carlo implementation of dynamic color screening via multiple exchanges of semisoft gluons as a basic QCD mechanism to understand diffractive electron-proton scattering at the HERA collider. Based on the kinematics of individual events in the standard QCD description of deep inelastic scattering at the parton level, which at low x is dominantly gluon initiated, the probability is evaluated for additional exchanges of softer gluons resulting in an overall color singlet exchange leading to a forward proton and a rapidity gap as the characteristic observables for diffractive scattering. The probability depends on the impact parameter of the soft exchanges and varies with the transverse size of the hard scattering subsystem and is therefore influenced by different QCD effects. We account for matrix elements and parton shower evolution either via conventional DGLAP log Q(2) evolution with collinear factorization or CCFM small x evolution with k(perpendicular to) factorization and discuss the sensitivity to the gluon density distribution in the proton and the importance of large log x contributions. The overall result is, with only two model parameters which have theoretically motivated values, a satisfactory description of the observed diffractive cross section at HERA obtained in a wide kinematical range.

Place, publisher, year, edition, pages
2016. Vol. 93, no 9, 094016
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
URN: urn:nbn:se:uu:diva-267309DOI: 10.1103/PhysRevD.93.094016ISI: 000376255900004OAI: oai:DiVA.org:uu-267309DiVA: diva2:872724
Funder
Swedish Research Council, 621-2011-5107 621-2013-4287
Available from: 2015-11-20 Created: 2015-11-20 Last updated: 2016-07-12Bibliographically approved
In thesis
1. Color Screening in QCD and Neutrinos from Singlino Dark Matter
Open this publication in new window or tab >>Color Screening in QCD and Neutrinos from Singlino Dark Matter
2015 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

Hard diffraction in proton collisions, where the initial state proton emerges from the interaction rather undisturbed despite a hard interaction scale, has been studied for a few decades. First observed in proton-proton collisions, the phenomenon is seen as well in deep inelastic electron-proton scattering (DIS) as a leading final state proton and a rapidity gap-region without final state particles. Although a rather successful description in terms of the exchange of a hadronic color singlet pomeron with a parameterized gluon content exists, it is still an open question whether a theoretically more well-founded description can be obtained based on quantum chromodynamics. The soft color interaction model (SCI) attempts this through additional gluon exchanges at momentum scales below the conventional scale of perturbative QCD and the hadronization scale. Such gluons can lead to an effective color singlet exchange and therefore to diffraction. This thesis explores the phenomenology of the SCI model in diffractive W and photon+jet production. For diffractive deep inelastic scattering, a dynamic color screening model is developed based on a summed amplitude for soft gluon exchanges. The studies of the model within Monte Carlo event simulation show that the additional dynamics improve the description of electron-positron scattering data from HERA.

Dijet events in proton-proton collisions with an upper limit on the energy flow between the jets is sensitive to large angle gluon emissions. This thesis applies a resummation method which takes into account also secondary emissions to describe this observable and shows that a good description of data from ATLAS can be achieved.

Supersymmetric extensions to the Standard Model provide a possible explanation for dark matter in the universe. The next-to-minimal supersymmetric extension (NMSSM) can contain a dark matter candidate in form of the lightest neutralino with a substantial singlino component. This thesis studies the prospects for indirect detection of dark matter for such viable NMSSM model points via the observation of neutrinos from neutralino annihilation in the sun with IceCube and the future extension PINGU. It is shown that with a few years of data taking large parts of the parameter space can be excluded or a discovery be made.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2015. 62 p.
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1321
Keyword
QCD, Diffraction, SCI, Dark Matter, Singlino, NMSSM, Indirect Detection
National Category
Physical Sciences
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-267310 (URN)978-91-554-9417-9 (ISBN)
Public defence
2016-01-20, 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2015-12-16 Created: 2015-11-20 Last updated: 2016-01-13

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Publisher's full texthttp://arxiv.org/abs/1511.06317

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Ingelman, GunnarWerder, Dominik

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