Search for the Standard Model Higgs boson in the H -> WW(*) -> l nu l nu decay mode with 4.7 /fb of ATLAS data at sqrt(s) = 7 TeV

TL;DR

The paper reports a search for the Standard Model Higgs boson decaying to $WW^{(*)}\to\ell\nu\ell\nu$ using the ATLAS detector with $4.7\,\mathrm{fb}^{-1}$ of 7 TeV data. It employs a multi-jet channel strategy and a transverse-mass fit to maximize sensitivity across low and high $m_H$, with data-driven control regions to constrain major backgrounds. No significant excess is observed, leading to a 95% CL exclusion of $m_H$ in the range 133–261 GeV (expected 127–233 GeV). The analysis demonstrates a rigorous combination of MC modeling, data-driven background normalization, and a profile likelihood framework to set Higgs limits in the $WW$ decay channel.

Abstract

A search for the Standard Model Higgs boson in the H -> WW(*) -> l nu l nu (l = e, mu) decay mode is presented. The search is performed using proton-proton collision data corresponding to an integrated luminosity of 4.7 /fb at a centre-of-mass energy of 7 TeV collected during 2011 with the ATLAS detector at the Large Hadron Collider. No significant excess of events over the expected background is observed. An upper bound is placed on the Higgs boson production cross section as a function of its mass. A Standard Model Higgs boson with mass in the range between 133 GeV and 261 GeV is excluded at 95% confidence level, while the expected exclusion range is from 127 GeV to 233 GeV.

Figures (3)

• Figure 1: Multiplicity of jets within the acceptance described in the text, for events satisfying the pre-selection criteria. The lepton flavours are combined. The hashed area indicates the total uncertainty on the background prediction. The expected signal for a SM Higgs boson with $m_{H}=125\mathrm{\ Ge V} \textrm{Ge V}$ is superimposed (multiplied by a factor 10 for better visibility).
• Figure 2: Transverse mass, $m_{\rm T}$, distribution in the 0-jet (top) and 1-jet (bottom) channels, for events satisfying all criteria for the low $m_{H}$ selection. The lepton flavours are combined. The expected signal for a SM Higgs boson with $m_{H}=125\mathrm{\ Ge V} \textrm{Ge V}$ is superimposed. The hashed area indicates the total uncertainty on the background prediction.
• Figure 3: Observed (solid) and expected (dashed) 95% CL upper limits on the Higgs boson production cross section, normalised to the SM cross section, as a function of $m_{H}$, over the full mass range considered in this analysis (top) and restricted to the range $m_{H} < 150\mathrm{\ Ge V} \textrm{Ge V}$ (bottom). The inner (green) and outer (yellow) regions indicate the $\pm 1\sigma$ and $\pm 2\sigma$ uncertainty bands on the expected limit, respectively. The results for nearby masses are highly correlated due to the limited mass resolution (5--8 Ge V, as inferred from a study of the effect of a hypothetical $m_{H}=125\mathrm{\ Ge V} \textrm{Ge V}$ signal on the behaviour of $q_{\mu}(\mu=1)$ as a function of $m_{H}$) in this final state.