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Color Screening in QCD and Neutrinos from Singlino Dark Matter
Uppsala University, Disciplinary Domain of Science and Technology, Physics, Department of Physics and Astronomy, High Energy Physics.
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 [en]
QCD, Diffraction, SCI, Dark Matter, Singlino, NMSSM, Indirect Detection
National Category
Physical Sciences
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
URN: urn:nbn:se:uu:diva-267310ISBN: 978-91-554-9417-9 (print)OAI: oai:DiVA.org:uu-267310DiVA: diva2:872725
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
List of papers
1. Diffractive W-+/- production at hadron colliders as a test of color singlet exchange mechanisms
Open this publication in new window or tab >>Diffractive W-+/- production at hadron colliders as a test of color singlet exchange mechanisms
2013 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 87, no 9, 094017- p.Article in journal (Refereed) Published
Abstract [en]

We revisit diffractive and exclusive (WX)-X-+/- production at hadron colliders in different models for soft color exchanges. The process pp -> p[(WX)-X-+/-]p, and in particular a W-+/- charge asymmetry, has been suggested as a way to discriminate diffractive processes as being due to pomeron exchange in Regge phenomenology or QCD-based color reconnection models. Our detailed analysis of the latter models at LHC energies shows, however, that they give similar results as pomeron models for leading protons and central (WX)-X-+/- production, including a vanishing W-+/- charge asymmetry. We demonstrate that soft color exchange models provide a continuous transition from diffractive to inelastic processes and thereby include the intrinsic asymmetry of inelastic interactions while being at the same time sensitive to the underlying hadronization models. Such sensitivity also concerns the differential distributions in proton momentum and W-+/- transverse momentum, which opens possibilities to discriminate between different color reconnection models.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-202368 (URN)10.1103/PhysRevD.87.094017 (DOI)000319126500001 ()
Available from: 2013-06-24 Created: 2013-06-24 Last updated: 2017-12-06Bibliographically approved
2. Diffractive W production in SCI models
Open this publication in new window or tab >>Diffractive W production in SCI models
2013 (English)In: PoS, Vol. EPS-HEP2013, 470- p.Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-264527 (URN)
Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2016-01-13
3. Probing the Pomeron structure using dijets and gamma plus jet events at the LHC
Open this publication in new window or tab >>Probing the Pomeron structure using dijets and gamma plus jet events at the LHC
2013 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 88, no 7, 074029- p.Article in journal (Refereed) Published
Abstract [en]

We consider hard diffractive events in proton-proton collisions at the LHC, in which both protons escape the collision intact. In such double Pomeron exchange processes, we propose to measure dijets and photon-jet final states, and we show that it has the potential to pin down the Pomeron quark and gluon contents, a crucial ingredient in the standard QCD description of hard diffraction. By comparing with predictions of the soft color interaction approach, we also show that more generally, the measurement of the photon-jet to dijet cross section ratio can put a stringent test on the QCD dynamics at play in diffractive processes in hadronic collisions.

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-211446 (URN)10.1103/PhysRevD.88.074029 (DOI)000326110400005 ()
Available from: 2013-11-27 Created: 2013-11-25 Last updated: 2017-12-06Bibliographically approved
4. Dynamic colour screening in diffractive deep inelastic scattering
Open this publication in new window or tab >>Dynamic colour screening in diffractive deep inelastic scattering
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.

National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-267309 (URN)10.1103/PhysRevD.93.094016 (DOI)000376255900004 ()
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
5. A QCD description of the ATLAS jet veto measurement
Open this publication in new window or tab >>A QCD description of the ATLAS jet veto measurement
Show others...
2013 (English)In: Physical Review D, ISSN 1550-7998, E-ISSN 1550-2368, Vol. 87, no 5, 054016- p.Article in journal (Refereed) Published
Abstract [en]

We present a new QCD description of the ATLAS jet veto measurement, using the Banfi-Marchesini-Smye equation to constrain the interjet QCD radiation. This equation resums emissions of soft gluons at large angles, at leading-logarithmic accuracy, and accounts for both the so-called Sudakov and nonglobal logarithms. We show that this approach is able to reproduce, with no fitting parameters, the fraction of high-p(T) forward-backward dijet events which do not contain additional hard emissions in the interjet rapidity range. We also compute the gap fraction in fixed-order perturbation theory to O(alpha(2)(s)) and show that the perturbative series is unstable at large rapidity intervals. 

National Category
Natural Sciences
Identifiers
urn:nbn:se:uu:diva-198388 (URN)10.1103/PhysRevD.87.054016 (DOI)000316108400008 ()
Available from: 2013-04-15 Created: 2013-04-15 Last updated: 2017-12-06Bibliographically approved
6. QCD description of ATLAS jet veto data
Open this publication in new window or tab >>QCD description of ATLAS jet veto data
2013 (English)In: PoS, Vol. EPS-HEP2013, 060- p.Article in journal (Refereed) Published
National Category
Physical Sciences
Identifiers
urn:nbn:se:uu:diva-264526 (URN)
Conference
EPS-HEP2013
Available from: 2015-10-14 Created: 2015-10-14 Last updated: 2016-01-13
7. Prospects for higgsino-singlino dark matter detection at IceCube and PINGU
Open this publication in new window or tab >>Prospects for higgsino-singlino dark matter detection at IceCube and PINGU
2015 (English)Article in journal (Refereed) Submitted
Abstract [en]

We study neutralino dark matter (DM) with large singlino fractions in the next-to-minimal supersymmetric Standard Model (NMSSM). We perform a detailed analysis of the parameter space regions of the model that yield such DM while satisfying the constraints from the Higgs boson searches at the Large Electron Proton (LEP) collider and the Large Hadron Collider (LHC) as well as from b-physics experiments. We find that this DM can yield a thermal relic density consistent with the Planck measurement in mass regions where the lightest neutralino of the minimal supersymmetric Standard Model (MSSM) generally cannot. This is particularly true for lighter DM masses, either less than 10 GeV or between 60 -100 GeV, and for heavier DM masses, between 500 - 1000 GeV. We then analyse the prospects for indirect detection of such DM at the IceCube neutrino telescope, assuming the complete 86-string configuration including DeepCore. We also consider the added sensitivity to low-mass DM with the proposed PINGU extension. We find that IceCube is sensitive to some regions of the NMSSM parameter space containing singlino-dominated DM and that a subset of such model points are already ruled out by the IceCube one-year data. IceCube will also be sensitive to some parameter space regions that will not be probed by the upcoming ton-scale direct detection experiments.

Keyword
Dark matter, supersymmetry, IceCube experiment, neutrino telescope, singlino, higgsino
National Category
Subatomic Physics Astronomy, Astrophysics and Cosmology
Research subject
Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-256039 (URN)
Funder
Swedish Research Council, 2007-4071Swedish Research Council, 621- 2011-5107Swedish Research Council, 621-2011-5109Swedish National Infrastructure for Computing (SNIC), SNIC 2014/1-5Swedish National Infrastructure for Computing (SNIC), p2013257
Available from: 2015-06-22 Created: 2015-06-22 Last updated: 2016-01-13

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