McGowan, Jamie Wythen;
(2023)
Approximate N³LO Parton Distribution Functions: In the pursuit of theoretical uncertainties...
Doctoral thesis (Ph.D), UCL (University College London).
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Abstract
This thesis presents the first global analysis of parton distribution functions (PDFs) at approximate N³LO in the strong coupling constant α, extending beyond the current highest NNLO achieved in PDF fits. To achieve this, a general formalism for the inclusion of theoretical uncertainties from missing higher orders (MHOs) in a PDF fit is established. By using the currently available knowledge surrounding the next highest order (N³LO) in α, consistent, justifiable and explainable approximate N³LO (aN³LO) PDFs are constructed, including estimates for missing higher order uncertainties (MHOUs). Specifically, N³LO approximations for splitting functions, transition matrix elements, coefficient functions and K-factors for multiple processes are introduced. Crucially, these are constrained to be consistent with the wide range of already available information about N³LO to match the complete result at this order as accurately as possible. Using this approach, this thesis includes results from a fully consistent approximate N³LO global fit within the MSHT framework. This relies on an expansion of the Hessian procedure used in previous MSHT fits to allow for sources of theoretical uncertainties. These are included as nuisance parameters in a global fit, controlled by knowledge and intuition based prior distributions. The differences between these aN³LO PDFs and the standard NNLO MSHT20 PDF set are investigated, as well as the impact of using aN³LO PDFs on the LHC production of a Higgs boson at this order. Alongside this, guidelines are provided on how these PDFs should be be used in phenomenological investigations. Finally, the effect of fitting to recent high-x datasets currently not included as standard in the MSHT20 global fit is discussed, with a focus on aN³LO PDFs at high-x.
| Type: | Thesis (Doctoral) |
|---|---|
| Qualification: | Ph.D |
| Title: | Approximate N³LO Parton Distribution Functions: In the pursuit of theoretical uncertainties... |
| Open access status: | An open access version is available from UCL Discovery |
| Language: | English |
| Additional information: | Copyright © The Author 2022. Original content in this thesis is licensed under the terms of the Creative Commons Attribution 4.0 International (CC BY 4.0) Licence (https://creativecommons.org/licenses/by/4.0/). Any third-party copyright material present remains the property of its respective owner(s) and is licensed under its existing terms. Access may initially be restricted at the author’s request. |
| UCL classification: | UCL UCL > Provost and Vice Provost Offices > UCL BEAMS UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Physics and Astronomy |
| URI: | https://discovery.ucl.ac.uk/id/eprint/10167783 |
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