Search for the Higgs boson in the H->WW(*)->lvlv decay channel in pp collisions at sqrt(s) = 7 TeV with the ATLAS detector

TL;DR

This ATLAS study searches for the Standard Model Higgs boson in the H->WW(*)->ell nu ell nu decay channel using 2.05 fb^-1 of pp collisions at sqrt(s)=7 TeV. The analysis selects events with exactly two opposite-sign leptons and up to one jet, employing kinematic cuts and control regions to constrain backgrounds such as WW, ttbar, Z/γ*+jets, and W+jets; backgrounds are normalized via data-driven and simulation-based methods. A profile likelihood with the CLs prescription is used to set 95% confidence level upper limits on sigma_H x BR(H->WW(*)->ell nu ell nu) as a function of m_H across 110–300 GeV; no significant excess is observed (largest deviation ~1.9 sigma). The results exclude a Standard Model Higgs boson in the range 145 < m_H < 206 GeV at 95% CL, contributing to narrowing the allowed mass window in early LHC Higgs searches.

Abstract

A search for the Higgs boson has been performed in the H->WW->lvlv channel (l=e/mu) with an integrated luminosity of 2.05/fb of pp collisions at sqrt(s) = 7 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<mH<300 GeV. The observations exclude the presence of a Standard Model Higgs boson with a mass 145<mH<206 GeV at 95% confidence level.

Figures (2)

• Figure 1: Distributions of $m_{\ell\ell}$ (left), $\Delta\phi_{\ell\ell}$ (center), and $m_{\rm T}$ (right). The top row shows the selection for the $H+0$-jet channel and the bottom row for the $H+1$-jet channel. The left and central plots are shown after the $p_{\rm T}^{\ell\ell}$ selection for the $H+0$-jet channel and after the $|{\bf p}_{\rm T}^{\rm tot}|$ cut for the $H+1$-jet channel. For the rightmost plots, the distributions are shown after all the cuts for $m_{H}=150$Ge V except the cut on $m_{\rm T}$ itself. The background distributions are stacked, so that the top of the diboson background coincides with the Standard Model (SM) line which includes the statistical and systematic uncertainties on the expectation in the absence of a signal. The expected signal for $m_H$=150 GeV is shown as a separate thicker line, and the final bin includes the overflow.
• Figure 2: The expected (dashed) and observed (solid) 95% CL 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.