A Search for the Higgs Boson Produced in Association With a Vector Boson Using the ATLAS Detector at the LHC

Abstract

This dissertation presents two searches for the Standard Model Higgs boson produced in association with a vector boson and decaying via $H\to b\bar{b}$. Specifically, the processes are: \llbb\ alone, and again in combination with the \vvbb\ and \lvbb\ processes. The dataset used for the analysis consists of 4.7 fb$^{-1}$ at $\sqrt{s} = $7~TeV and 20.3 fb$^{-1}$at $\sqrt{s} = $8~TeV from LHC collisions. The search was optimized without bias to a particular mass of the Standard Model Higgs boson. Background processes contributing to the total number of observed events are estimated using a combination of Monte Carlo simluation and data-driven techniques. Utilizing a maximum-likelihood analysis, an observed upper limit on the cross section at the 95% confidence interval for the \llbb\ channel is set at 2.76 times the Standard Model cross section with an expected limit of 2.54, and the observed upper limit for the combined search is 2.3 times the Standard Model cross section, with an expected limit of 1.01. Furthermore, compatibility with the Standard Model expectation is evaluated through the parameter $\mu$ = $\frac{\sigma_{observed}}{\sigma_{Standard Model}}$ and found to be $0.17\pm1.4$ for the \llbb\ analysis, and $1.09\pm0.61$ for the combined analysis, both consistent with the Standard Model expectation of 1.