Combined Higgs Analysis and Particle Identification Studies at ATLAS

A statistical combination of the low mass search channels for the Standard Model (SM) Higgs boson at the ATLAS Experiment is presented. It is found that with 1 fb−1 of ATLAS data, the SM Higgs can be excluded between 130 GeV and 190 GeV, at or above the 95% Confidence Level. In the presence of signal, a 5$\sigma$ observation is expected between 125 GeV and 185 GeV for 10 fb−1 of data. The effect of systematic uncertainties on the discovery and exclusion sensitivities are presented. The discovery potential of the t¯tH(H to b¯b) decay mode of the SM Higgs is assessed and the discovery sensitivity is found to be 1.5$\sigma$ for 30 fb−1. It is shown that the use of a neural network can improve the exclusion potential of the t¯tH search by a factor 3, increasing the SM cross-section excluded at 95% CL, with 1 fb−1 of expected ATLAS data, from 14.6$\sigma$t¯tH to 4.6$\sigma$t¯tH. A study of ATLAS particle identification efficiencies is also presented. A tool which applies these efficiencies to the output of the ATLAS fast simulation tool, ATLFast, has been developed. It is shown for isolated electrons from a t¯t sample that application of the electron identification efficiency improves the agreement between the fast and full simulation from ±10% to ±5%.