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Towards solving the proton spin puzzle
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, Nuclear Physics.
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, Nuclear Physics.
(English)Manuscript (preprint) (Other academic)
National Category
Subatomic Physics
Identifiers
URN: urn:nbn:se:uu:diva-357642OAI: oai:DiVA.org:uu-357642DiVA, id: diva2:1239911
Available from: 2018-08-20 Created: 2018-08-20 Last updated: 2019-05-13
In thesis
1. The interplay between quark and hadronic degrees of freedom and the structure of the proton
Open this publication in new window or tab >>The interplay between quark and hadronic degrees of freedom and the structure of the proton
2018 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

We study the low-energy sector of the strong interaction which is the least understood part of the Standard Model, the theory that describes the interactions of all known particles. The ideal particles for this study are the proton and the neutron, collectively called the nucleon. They make up the nucleus of all the atoms of our world and understanding them has been of high priority ever since their discovery. We show that one cannot neglect the effects of other hadrons, such as neutrons and pions when studying the proton. A large part of the proton's hadronic wavefunction is shown to consist of the wavefunctions of other hadrons. In other words, when probing the proton there is a sizeable probability that one is probing some other hadron surrounding the proton as a quantum fluctuation.

The nucleon itself consists of elementary particles known as quarks and gluons, collectively called partons. Exactly how the properties of these partons make up the properties of the nucleon has been the subject of active research ever since their discovery. Two main issues are the flavor asymmetry of the proton sea and the spin structure of the nucleon. To address these questions we study the interplay between the partonic and hadronic degrees of freedom. We introduce a model based on a convolution between hadronic quantum fluctuations as described by chiral perturbation theory, and partonic degrees of freedom motivated by a physical model of the nucleon having only few physically constrained parameters.

We present the hadronic distribution functions and the parton distribution functions. The results are in agreement with a large set of experimental data. These include the structure functions of the proton and the neutron. Agreement with the sum rules of the spin structure functions offers new insight into the spin structure of the nucleon.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2018. p. 99
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1711
National Category
Subatomic Physics
Identifiers
urn:nbn:se:uu:diva-357911 (URN)978-91-513-0420-5 (ISBN)
Public defence
2018-10-10, 80101, 09:00 (English)
Opponent
Supervisors
Available from: 2018-09-17 Created: 2018-08-21 Last updated: 2018-10-02
2. Phenomenology of new Neutral Vector Bosons and Parton Distributions from Hadronic Fluctuations
Open this publication in new window or tab >>Phenomenology of new Neutral Vector Bosons and Parton Distributions from Hadronic Fluctuations
2019 (English)Doctoral thesis, comprehensive summary (Other academic)
Abstract [en]

The Higgs particle was first predicted in 1964, and was discovered in the summer of 2012 at the Large Hadron Collider (LHC). This discovery was the latest in a long list of successful Standard Model predictions spanning the last fifty years. However, some of the Standard Models predictions, such as massless neutrinos, are not in agreement with experiment. Thus, extensions of the Standard Model should be considered. Furthermore, some issues, such as how quarks are bound within the proton, are difficult to study from first principles.

In paper I and II of this thesis, a class of models that contains a new TeV scale neutral vector boson is studied. The parameter space of this class of models is constrained using electroweak precision constraints and 13 TeV LHC data. Gauge anomalies are cancelled both by choosing appropriate fermion charges, and by adding Green-Schwarz terms.

The Higgs mechanism is often studied at leading order, but there are also important radiative corrections. These radiative corrections, which change the ground state energy, can both be IR divergent and gauge dependent. In paper III it is shown how to solve both of these problems. In particular, IR divergences are shown to be spurious.

In paper IV of this thesis, rapidity gaps at the LHC are explained by using a colour singlet two-gluon ladder exchange (BFKL). These exchanges, together with a soft-gluon model, are implemented in a complete Monte Carlo simulation, and reproduce observed rapidity gaps at the LHC.

The momentum distributions of bound partons, quarks and gluons, are described by parton distribution functions (PDFs). In paper V and VI of this thesis, a physically motivated model for PDFs is presented. This model can reproduce proton structure function data, and gives a possible solution to the proton spin puzzle.

Place, publisher, year, edition, pages
Uppsala: Acta Universitatis Upsaliensis, 2019. p. 57
Series
Digital Comprehensive Summaries of Uppsala Dissertations from the Faculty of Science and Technology, ISSN 1651-6214 ; 1820
Keywords
QCD, Higgs, Gauge Symmetry, Standard Model, BFKL, PDF, DIS, Beyond the Standard Model, Colliders, Phenomenology, Effective Potential, Anomaly
National Category
Subatomic Physics
Research subject
Physics with specialization in Elementary Particle Physics; Physics with specialization in Elementary Particle Physics
Identifiers
urn:nbn:se:uu:diva-383273 (URN)978-91-513-0675-9 (ISBN)
Public defence
2019-08-30, Room 80101, Ångströmlaboratoriet, Lägerhyddsvägen 1, Uppsala, 13:15 (English)
Opponent
Supervisors
Available from: 2019-06-04 Created: 2019-05-13 Last updated: 2019-06-17

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