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Precise measurements of the W boson's mass and lepton flavour universality, and trigger development with the LHCb experiment at CERN
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Hunter, Ross (2022) Precise measurements of the W boson's mass and lepton flavour universality, and trigger development with the LHCb experiment at CERN. PhD thesis, University of Warwick.
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Official URL: http://webcat.warwick.ac.uk/record=b3913209
Abstract
In the electroweak sector of the Standard Model (SM), comparing precise measurements with predictions built on the SM's assumptions offers one of the principal avenues for indirect discoveries of new physics. The W boson mass, mW, is a key SM parameter that is notoriously difficult to measure at hadron colliders, and the lack of high-precision measurements of it limits the sector's discovery power. Meanwhile, the SM's fundamental property of lepton flavour universality (LFU) has been questioned by hints of discrepancy in recent measurements of rare B-meson decays and legacy tests of W-boson decays. This thesis presents two measurements using LHCb's 2016 data that address these important issues: first, a proof-of-principle extraction of mW that paves the way for a competitive legacy measurement; and second, a test of the W boson's LFU in decays to tau leptons and muons that, when completed, will validate and complement other recent measurements shedding light on previous LFU anomalies.
The value of mW was measured to be
mW = 80354 _ 23stat _ 10exp _ 17theory _ 9PDF MeV;
which is consistent with previous direct measurements and indirect SM predictions. It is not consistent with the very-recent CDF measurement, and therefore places LHCb in prime position to address this high-profile disagreement with a future measurement using all available data.
LHCb is currently undergoing commissioning for a fresh period of data-taking, which features a brand-new detector, a factor of five more collisions and a fully redesigned trigger system. The development of the trigger validation tool HltEfficiencyChecker is also presented, which plays a crucial role in facilitating trigger optimization that fully exploits the new detector, whilst also conforming to its constraints. This tool helped the collaboration decide that the new first-level trigger should be implemented with GPUs, and is now widely used in LHCb, as exemplified in the development of trigger selections for electroweak processes in Run 3 presented here.
Item Type: | Thesis (PhD) | ||||
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Subjects: | Q Science > QC Physics | ||||
Library of Congress Subject Headings (LCSH): | W bosons, Leptons (Nuclear physics), Mass (Physics), Quantum flavor dynamics, Hadron colliders, Standard model (Nuclear physics) | ||||
Official Date: | September 2022 | ||||
Dates: |
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Institution: | University of Warwick | ||||
Theses Department: | Department of Physics | ||||
Thesis Type: | PhD | ||||
Publication Status: | Unpublished | ||||
Supervisor(s)/Advisor: | Vesterinen, Mika | ||||
Format of File: | |||||
Extent: | xxii, 184 pages : illustrations, charts | ||||
Language: | eng |
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