2014 Theses Doctoral

Search for the Standard Model Higgs boson in Z + γ; final states with the ATLAS detector at the LHC

Tian, Feng

This dissertation describes a search for the Standard Model Higgs boson in Z+photon channel with the ATLAS detector at the LHC using 4.6 fb⁻¹ of proton-proton collisions at center of mass energy 7 TeV in 2011 and 20.7 fb⁻¹ of proton-proton collisions at center of mass energy 8 TeV in 2012. The distribution of the mass difference between M_Zphoton and M_Z is compared to the Standard Model (SM) background expectations. No significant deviation from the SM prediction is observed and the upper limits on the signal strength μ of a Higgs boson with a mass between 120 and 150 GeV are derived. The expected exclusion limits at 95% confidence level range between 7.3 and 22.3 times the predicted Standard Model cross section. The observed exclusion limits range between 5.3 and 38.7 times the Standard Model cross section. For a Higgs boson with mass of 125.5 GeV, the expected and observed limits are 13.2 and 17.0 times the Standard Model respectively.