Using displaced tracks to search for sterile neutrinos in the ATLAS detector
department or school: Science, Faculty of
department or school: Physics and Astronomy, Department of
data provider: DSpace
degree campus: UBCV
creator: Newhouse, Robin
issued: 2022-12-23T23:38:01Z
issued: 2022
related degree: Doctor of Philosophy - PhD
degree grantor: University of British Columbia
description: The Standard Model of particle physics is a powerful theory of nature, yet it does not account for all physical observations. Notably, the nonzero masses of the three neutrino flavours and their transformations into one another suggest the need for an extension of the Standard Model. One such extension postulates the existence of Heavy Neutral Leptons (HNLs, 𝑁) — right-handed neutrino states that do not interact with other particles except through mixing with Standard Model neutrinos. HNLs may generate light neutrino masses through the so-called “seesaw mechanism.” This dissertation presents a direct search for long-lived HNLs using 139 fb⁻¹ of √s=13 TeV pp collision data collected by the ATLAS detector at the Large Hadron Collider. In this search, the 𝑁 is produced via W → 𝑁 μ or W → 𝑁 e and decays into a neutrino and two charged leptons, which form a displaced vertex in the inner detector. No signal is observed, and limits are set on the squared mixing angles of the 𝑁 with the Standard Model neutrinos in the mass range 3 GeV < m𝘕 < 15 GeV. For the first time in a collider search, results are presented in the context of realistic HNL mixing models consistent with neutrino oscillation data. Such a displaced vertex search relies heavily upon nonstandard reconstruction algorithms. An additional pass of the track reconstruction algorithm with relaxed collision vertex pointing requirements is executed on a subset of the recorded data to improve sensitivity to long-lived particles in the inner detector. This Large-Radius Tracking (LRT) configuration is effective yet computationally expensive due to the reconstruction of many “fake” tracks not formed from individual charged particles. This algorithm was optimized in preparation for the Run 3 data-taking period, which began in July 2022. Fake LRT tracks are reduced by 95%, drastically improving the purity and reducing the computational load such that LRT is now run in the default reconstruction pipeline. This optimization …
aggregated CHO: https://circle.library.ubc.ca/rest/handle/2429/83521
note: Using displaced tracks to search forsterile neutrinos in the ATLAS detectorbyRobin NewhouseB.Sc., The University of British Columbia, 2015A THESIS SUBMITTED IN PARTIAL FULFILLMENT OFTHE REQUIREMENTS FOR THE DEGREE OFDOCTOR OF PHILOSOPHYinThe Faculty of Graduate and Postdoctoral Studies(Physics)THE UNIVERSITY OF BRITISH COLUMBIA(Vancouver)December 2022© Robin Newhouse 2022The following individuals certify that they have read, and recommend to the Faculty of Graduate andPostdoctoral Studies for acceptance, the thesis entitled:Using displaced tracks to search for sterile neutrinos in the ATLAS detectorsubmitted by Robin Newhouse in partial fulfillment of the requirements for the degree of Doctor ofPhilosophy in Physics.Examining Committee:Alison Lister, Associate Professor, Physics & Astronomy, UBCSupervisorJeremy Heyl, Professor, Physics & Astronomy, UBCSupervisory Committee MemberMichael Hasinoff, Professor, Physics & Astronomy, UBCUniversity ExaminerMichiel van de Panne, Professor, Computer Science, UBCUniversity ExaminerTodd Adams, Professor, Physics, Florida State UniversityExternal ExaminerAdditional Supervisory Committee:Colin Gay, Professor, Physics & Astronomy, UBCSupervisory Committee MemberAriel Zhitnitsky, Professor, Physics & Astronomy, UBCSupervisory Committee MemberiiAbstractThe Standard Model of particle physics is a powerful theory of nature, yet it does not account for all physicalobservations. Notably, the nonzero masses of the three neutrino flavours and their transformations into oneanother suggest the need for an extension of the StandardModel. One such extension postulates the existenceof Heavy Neutral Leptons (HNLs,N ) — right-handed neutrino states that do not interact with other particlesexcept through mixing with Standard Model neutrinos. HNLs may generate light neutrino masses throughthe so-called “seesaw mechanism.”This dissertation presents a direct search for long-lived HNLs using 139 fb−1 of√푠 = 13 TeV 푝푝 collisiondata collected by the A…
has type: Thesis/Dissertation
date issued: 2023-05
is shown at: 10.14288/1.0422904
language: eng
degree discipline: Physics
provider: Vancouver : University of British Columbia Library
publisher: University of British Columbia
rights: Attribution-NonCommercial-ShareAlike 4.0 International
rights URI: http://creativecommons.org/licenses/by-nc-sa/4.0/
scholar level: Graduate
contributor: Lister, Alison
type: Text
identifier URI: http://hdl.handle.net/2429/83521