# Dissertation/Thesis Abstract

Search for a Light Pseudoscalar Higgs Boson at √s = 13TeV with the CMS Detector
by Shi, Mengyao, Ph.D., University of California, Davis, 2019, 150; 13865343
Abstract (Summary)

A search for a light pseudoscalar Higgs boson ($\mathrm{a}$) is performed using the 2016 Large Hadron Collider (LHC) proton-proton collision data corresponding to an integrated luminosity of 35.9 fb-1 collected at √s = 13TeV by the CMS experiment. The search looks for gg ⟶ H and qq ⟶ qqH with H ⟶aa ⟶ μμττ, where H can be the 125 GeV state or a heavier one. Due to the large mass difference between the H and the a and lightness of the a decay products, the two pairs of μ and τ are highly boosted and collimated. A dedicated di-tau reconstruction technique is devised to increase the efficiency with respect to standard tau reconstruction algorithms. In the absence of a significant signal, model-independent limits are set at 95% C.L. on the branching fraction for H ⟶ aa ⟶ μμττ as a function of ma in the range 3.6 < ma < 21 GeV$, down to 1.5 x 10-4}$ for mH = 125 GeV, 2.0 x 10-4 for mH = 300 GeV, and 1.2 x 10-3 for mH = 750 GeV. Model-dependent limits are set within the context of two Higgs boson doublet plus singlet models, with the most stringent results obtained for Type-III models. These results are complementary to current LHC limits for heavier ma that lead to resolved final-state leptons.

Indexing (document details)
 Advisor: Chertok, Maxwell Commitee: Conway, John, Erbacher, Robin School: University of California, Davis Department: Physics School Location: United States -- California Source: DAI-B 81/3(E), Dissertation Abstracts International Source Type: DISSERTATION Subjects: Particle physics, Quantum physics Keywords: Publication Number: 13865343 ISBN: 9781088330135