Higgs Searches in the H -> WW Decay Mode Using the ATLAS Detector

The prospects for Higgs searches in the WW decay mode are investigated. Search strategies are presented for the channels H+0j and H+2j (where both W bosons decay to leptons), and for H+2j (with one W decaying to leptons and one to jets). Methods to extract the background normalization from data are discussed for all channels. With 10/fb of data, the H+0j channel can reach a 5 sigma discovery for a Standard Model (SM) Higgs with a mass between 145 and 180 GeV; the mass can be measured with a precision of about 2 GeV if the mass is around 160 GeV, or about 6 GeV if it is close to 140 GeV. The H+2j (dilepton) channel has a similar sensitivity, reaching the 5 sigma significance level for Higgs masses between 150 and 180 GeV and yielding a less precise mass determination. The sensitivity of the H+2j (lepton-hadron) channel peaks at about 350 GeV, where it is slightly below the 5 sigma level; the expected error on the mass determination at this mass is about 6 GeV. The combined sensitivity of the two dilepton channels is estimated, and a combined fit is presented which includes the channel where the Higgs decays to ZZ and then to four leptons. With 1/fb, the combined fit can exclude a SM Higgs with a mass above 145 GeV. At 10/fb, the expected significance is above the 5 sigma level for Higgs masses above 135 GeV.