A Search for New Low-Mass Diphoton Resonances at Atlas and an Investigation into Using Gaussian Process Regression to Model Non-resonant Two-Photon Standard Model Backgrounds / Rob Roy MacGregor Fletcher.

Format:

Book

Thesis/Dissertation

Author/Creator:

Fletcher, Rob Roy MacGregor, author.

Contributor:

Kroll, I. J., degree supervisor.

University of Pennsylvania. Physics and Astronomy, degree granting institution.

Language:

English

Subjects (All):

Physics.

Physics and astronomy--Penn dissertations.

Penn dissertations--Physics and astronomy.

Local Subjects:

Physics.

Physics and astronomy--Penn dissertations.

Penn dissertations--Physics and astronomy.

Genre:

Academic theses.

Physical Description:

1 online resource (227 pages)

Contained In:

Dissertations Abstracts International 80-07B.

Place of Publication:

[Philadelphia, Pennsylvania] : University of Pennsylvania ; Ann Arbor : ProQuest Dissertations & Theses, 2018.

Language Note:

English

System Details:

Mode of access: World Wide Web.

text file

Summary:

The Standard Model of particle physics has been tested over many years with many ex- periments and has predicted experimental results with remarkable accuracy. In 2012, the last piece of the Standard Model, the Higgs boson, was discovered by the experiments ATLAS and CMS at the Large Hadron Collider (LHC). Although this completes the Standard Model, this by no means completes our picture of the physics that describes the observable universe. Several phenomena and measurements remain unexplained by the Standard Model including gravity, dark matter, the baryon-antibaryon asymmetry of the universe and more. One of the primary goals of the LHC and the ATLAS experiment are to search for extensions and modifications to the Standard Model that could help to explain these phenomena. This thesis presents three areas where I made major contributions. The first is in the identification of prompt electrons in ATLAS using a likelihood method both in the online trigger system and in offline data analysis. Prompt electrons are ubiquitous in the signatures of electroweak physics, one of the cornerstones of the ATLAS physics program. Next I present a search for new physics in low-mass (65-110 GeV) diphoton events. This is a model independent search that is motivated by several extensions to the Standard Model including the two Higgs doublet model where new scalars can appear as lighter versions of the Standard Model Higgs. No evidence for a new narrow resonance is found, so limits ranging from 30 to 101 fb are set on the production cross section of such a resonance, assuming that its branching fraction to two photons is 100 percent. The sensitivity of these results are limited by the systematic uncertainties due to the potential spurious signals introduced by the two-photon non-resonant Standard Model background. My third contribution was an initial investigation of a new method to model this background using Gaussian Process Regression.

Notes:

Source: Dissertations Abstracts International, Volume: 80-07, Section: B.

Publisher info.: Dissertation/Thesis.

Advisors: Kroll, I. J.; Committee members: Cullen Blake; Justin Khoury; Elliot Lipeles; Evelyn Thomson.

Department: Physics and Astronomy.

Ph.D. University of Pennsylvania 2018.

Local Notes:

School code: 0175

ISBN:

9780438766600

Access Restriction:

Restricted for use by site license.

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