Search for the Higgs Boson in the $H\to W{W}^{(*)}\to l^{+}\nu l^{-}\overline{\nu }$ Decay Channel in $pp$ Collisions at $\sqrt{s}=7\mathrm{TeV}$ with the ATLAS Detector

A search for the Higgs boson has been performed in the $H\to W{W}^{(*)}\to {\ell }^{+}\nu {\ell }^{-}\overline{\nu }$ channel ($\ell =e/\mu$) with an integrated luminosity of $2.05{\mathrm{fb}}^{-1}$ of $pp$ collisions at $\sqrt{s}=7\mathrm{TeV}$ collected with the ATLAS detector at the Large Hadron Collider. No significant excess of events over the expected background is observed and limits on the Higgs boson production cross section are derived for a Higgs boson mass in the range $110\mathrm{GeV}<m_{\mathrm{H}}<300\mathrm{GeV}$. The observations exclude the presence of a standard model Higgs boson with a mass $145<m_{\mathrm{H}}<206\mathrm{GeV}$ at 95% confidence level.

Figure 1

Distributions of $m_{\ell \ell }$ (left), $\Delta {\varphi }_{\ell \ell }$ (center), and $m_{\mathrm{T}}$ (right). The top row shows the selection for the $H+0-\mathrm{jet}$ channel and the bottom row for the $H+1-\mathrm{jet}$ channel. The left and central plots are shown after the $p_{\mathrm{T}}^{\ell \ell }$ selection for the $H+0-\mathrm{jet}$ channel and after the $|{\mathbf{p}}_{\mathrm{T}}^{\mathrm{tot}}|$ cut for the $H+1-\mathrm{jet}$ channel. For the rightmost plots, the distributions are shown after all the cuts for $m_H=150\mathrm{GeV}$ except the cut on $m_{\mathrm{T}}$ itself. The background distributions are stacked, so that the top of the diboson background coincides with the standard model line which includes the statistical and systematic uncertainties on the expectation in the absence of a signal. The expected signal for $m_H=150\mathrm{GeV}$ is shown as a separate thicker line, and the final bin includes the overflow.

Figure 2

The expected (dashed) and observed (solid) 95% C.L. upper limits on the cross section, normalized to the standard model cross section, as a function of the Higgs boson mass. Expected limits are given for the scenario where there is no signal. The vertical lines in the curves indicate the points where the selection cuts change, and the bands around the dashed line indicate the expected statistical fluctuations of the limit.