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

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.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2023

Author dc:creator

• Rousso, David

Advisors dc:contributor.advisor

• Potter, Christina
• Brandt, Oleg

• ATLAS
• CERN
• displaced vertices
• Experimental Particle Physics
• Higgs portal
• ITk
• jets
• LHC
• Long-Lived Particles
• MET
• R-parity violation
• Run 2
• supersymmetry
• SUSY

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/dd324be8-8cd0-4762-b00b-e95f7381469a/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.104150

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/360964