Thesis
Measurements of ATLAS, measurements with ATLAS: construction and characterisation of ITk Pixel detector structures, and a search for leptoquarks in events with di-tau final states
- Abstract:
-
The Large Hadron Collider represents the energy frontier of the field of collider physics, and in recent years has produced some of the most precise measurements of the behaviour of fundamental particles. This thesis spans the lifecycle of a general-purpose particle detector: from a measurement and interpretation of data collected with the ATLAS detector, to the construction and characterisation of the ITk, a new inner tracker for ATLAS to address the challenges of the High-Luminosity era.
The ITk is one of the largest and most ambitious tracking detector projects to date, and faces a challenging new environment. The pixel detector comprises lightweight support structures populated with modules, and the construction and quality control of these is discussed with reference to half-rings for the Outer Endcap subdetector. Readout, control, monitoring, and safety systems have been developed that mirror the final detector services, and preliminary results demonstrate preparedness for the upcoming pre-production phase.
Precise knowledge of detector material is crucial both during the R&D phase and as an input to simulations. The first direct measurement of the radiation length of an ITk pixel module is presented, producing a 2D resolved map with O(10%) uncertainty and 0.5 mm ×0.5 mm resolution via a measurement of the multiple scattering of positrons at a testbeam. The understanding of our detector plays a key role in enabling the analysis of complex detector signatures, often in a search for new phenomena.
Probing off-shell production of new particles or tail effects encoded in effective field theory operators allows for searches for new phenomena beyond the naïve energy threshold of the LHC. A measurement of the Drell-Yan cross-section in a final state with two τ leptons in association with b-jets at high di-tau mass is combined with a search for leptoquark and Z′ boson models, using data collected by the ATLAS detector during Run 2 of the LHC. In addition, model-independent constraints are extracted on new physics contributions to operators involving τ leptons. The unfolded cross-section matches Standard Model predictions, and stringent constraints are set on new physics models which begin to exclude the mass-coupling regions preferred by recent hints of lepton flavour universality violating anomalies.
Actions
Authors
Contributors
- Institution:
- University of Oxford
- Division:
- MPLS
- Department:
- Physics
- Sub department:
- Particle Physics
- Oxford college:
- Brasenose College
- Role:
- Supervisor
- ORCID:
- 0000-0002-1287-4712
- Institution:
- University of Oxford
- Division:
- MPLS
- Department:
- Physics
- Sub department:
- Particle Physics
- Research group:
- ATLAS
- Role:
- Supervisor
- ORCID:
- 0000-0003-2371-9723
- Funder identifier:
- https://ror.org/0336mm561
- Funding agency for:
- Koch, SF
- Grant:
- Clarendon Scholarship
- Programme:
- Clarendon Fund
- Funder identifier:
- https://ror.org/057g20z61
- Funding agency for:
- Koch, SF
- Grant:
- ST/W507726/1
- Programme:
- Doctoral Training Grant
- Funding agency for:
- Koch, SF
- Grant:
- Hector Pilling Scholarship
- DOI:
- Type of award:
- DPhil
- Level of award:
- Doctoral
- Awarding institution:
- University of Oxford
- Language:
-
English
- Keywords:
- Subjects:
- Deposit date:
-
2025-09-28
Terms of use
- Copyright holder:
- Simon Florian Koch
- Copyright date:
- 2025
- Rights statement:
- This thesis is licensed under a Creative Commons Attribution 4.0 International License, which permits use, sharing, adaptation, distribution and reproduction in any medium or format, as long as you give appropriate credit to the original author and the source, provide a link to the Creative Commons licence, and indicate if changes were made. The images or other third party material in this work are included in the work’s Creative Commons licence, unless indicated otherwise.
- Licence:
- CC Attribution (CC BY)
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