Observation and measurement of Higgs boson decays to $WW^*$ with the ATLAS etector

We report the observation of Higgs boson decays to $\WWs$ based on an excess over background of $\HwwSignif{obs}{all}$ standard deviations in the dilepton final state, where the Standard Model expectation is $\HwwSignif{exp}{all}$ standard deviations. Evidence for the vector-boson fusion (VBF) production process is obtained with a significance of $\HwwSignif{obs}{VX}$ standard deviations. The results are obtained from a data sample corresponding to an integrated luminosity of $\HwwLumi{0}{0}\ifb$ from $\sqrt{s}{\EQ}7$ and $8\TeV$ $pp$ collisions recorded by the ATLAS detector at the LHC. For a Higgs boson mass of $\HwwHiggsMass{ATLAS}\GeV$, the ratio of the measured value to the expected value of the total production cross section times branching fraction is $1.09^{+0.16}_{-0.15}\,\textrm{(stat)}^{+0.17}_{-0.14}\,\textrm{(syst)}$. The corresponding ratios for the gluon fusion and vector-boson fusion production mechanisms are $1.02{\PM}0.19\,\textrm{(stat)}\,^{+0.22}_{-0.18}\,\textrm{(syst)}$ and $1.27\,^{+0.44}_{-0.40}\,\textrm{(stat)}\,^{+0.30}_{-0.21}\,\textrm{(syst)}$, respectively. At $\sqrt{s}{\EQ}8\TeV$, the total production cross sections are measured to be $\sigma(gg{\TO}\HWW) = 4.6{\PM}0.9\,\textrm{(stat)}\,^{+0.8}_{-0.7}\,\textrm{(syst)}\pb$ and $\sigma(\VBF~\HWW){\EQ}0.51\,^{+0.17}_{-0.15}\,\textrm{(stat)}\,^{+0.13}_{-0.08}\,\textrm{(syst)}\pb$. The fiducial cross section is determined for the gluon-fusion process in exclusive final states with zero or one associated jet.