Search for a Standard Model Higgs Boson in the $H\to ZZ\to {\ell }^{+}{\ell }^{-}\nu \overline{\nu }$ Decay Channel with the ATLAS Detector

A search for a heavy standard model Higgs boson decaying via $H\to ZZ\to {\ell }^{+}{\ell }^{-}\nu \overline{\nu }$, where $\ell =e$, $\mu$, is presented. It is based on proton-proton collision data at $\sqrt{s}=7\mathrm{TeV}$, collected by the ATLAS experiment at the LHC in the first half of 2011 and corresponding to an integrated luminosity of $1.04{\mathrm{fb}}^{-1}$. The data are compared to the expected standard model backgrounds. The data and the background expectations are found to be in agreement and upper limits are placed on the Higgs boson production cross section over the entire mass window considered; in particular, the production of a standard model Higgs boson is excluded in the region $340<m_H<450\mathrm{GeV}$ at the 95% confidence level.

Figure 1

The dilepton invariant mass distribution for events with exactly two oppositely charged electrons or muons. The inset at the bottom of the figure shows the ratio between the data and the combined background expectations as well as a band corresponding to the combined systematic uncertainties of the analysis.

Figure 2

The $E_T^{\mathrm{miss}}$ (left) and $\Delta \varphi (\ell ,\ell )$ (right) distributions for events with exactly two oppositely charged electrons or muons inside the $Z$ mass window. The insets at the bottom show the ratio between data and the combined background expectations as well as a band corresponding to the combined systematic uncertainties of the analysis.

Figure 3

The transverse mass distribution of $H\to ZZ\to {\ell }^{+}{\ell }^{-}\nu \overline{\nu }$ candidates in the high $m_H$ search region for the data (dots), the expected backgrounds (histograms) and a Higgs boson of mass 380 GeV (filled histogram). The electron and muon channels are combined.

Figure 4

Observed and expected 95% confidence level upper limits on the Higgs boson production cross section divided by the SM prediction. The green and yellow bands indicate the $\pm 1\sigma$ and $\pm 2\sigma$ fluctuations, respectively, around the median sensitivity. The limits are based on $1.04{\mathrm{fb}}^{-1}$ of data at $\sqrt{s}=7\mathrm{TeV}$.