자료유형  

 학위논문

Control Number  

0017164643

International Standard Book Number  

9798346857112

Dewey Decimal Classification Number  

593.7

Main Entry-Personal Name  

MacKenzie, Michael.

Publication, Distribution, etc. (Imprint  

[S.l.] : Northwestern University., 2024

Publication, Distribution, etc. (Imprint  

Ann Arbor : ProQuest Dissertations & Theses, 2024

Physical Description  

325 p.

General Note  

Source: Dissertations Abstracts International, Volume: 86-06, Section: B.

General Note  

Advisor: Velasco, Mayda.

Dissertation Note  

Thesis (Ph.D.)--Northwestern University, 2024.

Summary, Etc.  

요약The search for lepton flavor violation has a long history in particle physics, starting from the search for µ → eγ after the discovery of the muon. Lepton flavor was a conserved quantity in the Standard Model until the discovery of neutrino flavor oscillations showed that neutrinos are not massless, and consequentially lepton flavor conservation is violated in nature. Despite this, lepton flavor violation has never been observed in the charged sector and the predicted rates of flavor violation in the charged lepton sector are well below the observable level at any current or future high energy experiment due to the small neutrino masses.Many models beyond the Standard Model predict measurable rates of charged lepton flavor violation (CLFV), where the observation of such a process would be unambiguous evidence of new physics. This thesis presents a search for CLFV Z boson decays at the Compact Muon Solenoid (CMS) experiment at the Large Hadron Collider (LHC). The search utilizes the Run 2 dataset of 13 TeV center-of-mass energy proton-proton collisions, corresponding to an integrated luminosity of 138 fb−1. The Z → eµ, Z → eτ , and Z → µτ decays are each separately searched for. The Z → eµ decay search is performed using exclusive categories defined using machine learning techniques to create signal enriched regions, where the eµ invariant mass distributions are simultaneously fit. The Z → eτ and Z → µτ searches use different-flavor leptonic and hadronic tau decay categories, where machine learning techniques are used to create an observable per category that is simultaneously fit in the tau final state categories for each search. The Z → eµ search is extended into a search for a new Z-like (Z' ) boson resonance in the eµ data within the mass range 110 to 500 GeV/c2. The measured (expected) 95% CLS upper limits on these CLFV decay branching fractions are: B(Z → eµ) 1.9 (2.0) x 10−7, B(Z → eτ ) 13.8 (11.4) x 10−6, and B(Z → µτ ) 12.0 (5.3)x10−6. The observed Z → eµ limit is the most stringent limit to date on this process. No significant Z' → eµ resonance signature is observed within the 110 to 500 GeV/c2 mass range, placing a 95% confidence level exclusion limit of 0.5 − 10 fb on the total σ(Z' )·B(Z' → eµ) cross section within this range. All three CLFV Z decay searches found rates of CLFV consistent with the Standard Model, though the Z → µτ search observed a notable 2.7σ excess. This observation motivates further testing utilizing the Run 3 CMS dataset, where the Run 2+3 combined dataset corresponds to more than double the integrated luminosity of the Run 2 dataset alone.

Subject Added Entry-Topical Term  

Particle physics.

Subject Added Entry-Topical Term  

Nuclear physics.

Subject Added Entry-Topical Term  

Physics.

Index Term-Uncontrolled  

Charged lepton flavor violation

Index Term-Uncontrolled  

Proton-proton collisions

Index Term-Uncontrolled  

Neutrinos

Index Term-Uncontrolled  

Boson resonance

Index Term-Uncontrolled  

Large Hadron Collider

Added Entry-Corporate Name  

Northwestern University Physics and Astronomy

Host Item Entry  

Dissertations Abstracts International. 86-06B.

Electronic Location and Access  

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Control Number  

joongbu:656438