  We report results of a study of the Standard Model Higgs boson discovery
potential through the W-pair leptonic decay modes with the ATLAS detector at
LHC at 14 TeV center-of-mass energy. We used MC samples with full detector
simulation and reconstruction of the ATLAS experiment to estimate the ATLAS
detection sensitivity for the reaction of pp -> H -> WW -> e\nu \mu\nu with no
hard jet or two hard jets in the final states. The prospects for the Higgs
boson searches at ATLAS are presented, including trigger efficiencies and
data-driven methods to estimate the backgrounds using control samples in data.
With 10/fb of integrated luminosity, one would expect to discover a Standard
Model Higgs boson with ATLAS detector in Higgs boson mass range 135 < m_H < 190
GeV. If the Higgs boson does not exist, we will extend and confirm the
exclusion produced by the Tevatron Higgs boson search result, which has ruled
out the Higgs boson mass range of 160 < m_H < 170 GeV at 95% confidence level.
If Higgs boson would be discovered, ATLAS could measure its mass with a
precision of about 2 and 7 GeV for Higgs boson mass around 160 GeV and 130 GeV,
respectively.
