Abstracts Category : Other

Search for the Standard Model Higgs boson produced inassociation with top quarks in the lepton plus jets channel

by Sean Christopher Flowers

Results for the search of a Higgs boson decaying to abottom quark-antiquark pair producedwith a top quark-antiquark pair(t tH) in the lepton plus jets channel in proton-protoncolli-sions at a center-of-mass energy of vs = 13 TeV arepresented. The data used correspondsto an integrated luminosity of12.9 fb-1 recorded with the CMS experiment in 2016. Toincrease thesensitivity of the search, selected events are categorized bynumber of jets andnumber of b-tagged jets resulting in differentexpected signal and background rates. Foreach category twomultivariate techniques are combined to separate the signal andback-ground events. A machine learning process called a boosteddecision tree (BDT) is trainedon the two types of classes of eventsand then split into high and low purity based on theoutput. Thephysics motivated matrix element method (MEM) is applied to the BDTout-put to obtain the final two dimensional discriminator. Theresult is presented in terms ofthe t tH signal strength modifier, the ratio of the observed t tH production cross sectionrelativeto the expected cross section based on a 125 GeV Standard ModelHiggs boson. Acombined fit of the final discriminant in allcategories of the lepton plus jets channel resultsan observed(expected) upper limit of < 1.8(2.1+1.0) at the 95% confdiencelevel. The -0.6best-fit value of the signal strength modifier isfound to be -0.43+1.02.Advisors/Committee Members: Winer, Brian (Advisor).