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oai:www.repository.cam.ac.uk:1810/3609642023-12-22T14:27:04Zcom_1810_198332com_1810_256064col_1810_214775

Searching for long-lived particles Beyond the Standard Model with displaced vertex signatures using the ATLAS detector: Not all hopes for new physics die immediately https://doi.org/10.17863/CAM.104150 Rousso, David Potter, Christina Brandt, Oleg Traditional LHC searches assume that Beyond the Standard Model particles decay immediately after they are produced. However, there is no a priori motivation for this assumption. This thesis details part of the growing effort to use new unorthodox signatures to search for models where these particles are long-lived. All searches were conducted with the full 139 fb¯¹ of Run 2 data taken in 2015-2018. The first analysis uses displaced vertex signatures in multijet-triggered events to search for long-lived particles that decay into hadrons in the ATLAS inner detector. This was the first such Run 2 search, placing the best limits in this lifetime range to date on R-parity violating supersymmetry models. The second analysis uses a similar strategy, but using missing transverse energy as the trigger. This improves upon the early Run 2 2016-data search with an updated analysis strategy and a new vertexing algorithm. A focus on interpreting this search with the the Higgs Portal model predicts sensitivity to the exclusion of the Higgs branching ratio to hadronically-decaying long-lived particles to the lowest limit to date. As an outlook to the future of displaced vertex analyses using the ATLAS inner tracker upgrade (ITk), a script library is also described for the automation of quality control for its strip sensors. University of Cambridge 2023-07-28 Thesis Doctoral Doctor of Philosophy (PhD) eng Gates Cambridge https://www.repository.cam.ac.uk/handle/1810/360964 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/4eb20de0-9f27-4c2d-82a3-066c6a69b13e/download ba6c8c6fd63e81e005ee30300956d8a9 https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/dd324be8-8cd0-4762-b00b-e95f7381469a/download 87eda9de84448d1f82354d60eee3eb5f https://www.rioxx.net/licenses/all-rights-reserved/ ATLAS CERN displaced vertices Experimental Particle Physics Higgs portal ITk jets LHC Long-Lived Particles MET R-parity violation Run 2 supersymmetry SUSY