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How to find a Higgs Boson with a Mass between 155--180 GeV at the LHC

M. Dittmar, H. Dreiner

TL;DR

This paper addresses the challenge of discovering a Standard Model Higgs boson in the mass range 155-180 GeV at the LHC, where decays to on-shell W pairs dominate but produce no sharp mass peak. The authors advocate using the fully leptonic decay H->W+W-->(l nu)(l' nu) as a discovery channel, including tau decays, and simulate signal and backgrounds with PYTHIA to account for hadronization and detector-level effects. They develop a sequence of cuts that exploit kinematic features and spin correlations of Higgs decays (e.g., dilepton opening angles, cos theta* distribution, jet veto, MET, and WW mass estimates) to suppress irreducible WW and ttbar backgrounds. They show that a signal-to-background ratio near unity and a discovery significance of 5-10 sigma can be achieved with about 5 fb-1 of data at 14 TeV, outperforming the ZZ*->4l channel in this mass window. These results suggest a fast, robust Higgs discovery path for ATLAS/CMS in this challenging mass window.

Abstract

We reconsider the signature of events with two charged leptons and missing energy as a signal for the detection of the Standard Model Higgs boson in the mass region M(Higgs)=155--180 GeV. It is shown that a few simple experimental criteria allow to distinguish events originating from the Higgs boson decaying to H --> W+W- from the non resonant production of W+W- X at the LHC. With this set of cuts, signal to background ratios of about one to one are obtained, allowing a 5--10 sigma detection with about 5~fb-1 of luminosity. This corresponds to less than one year of running at the initial lower luminosity L= 10**33/ cm**2/sec. This is significantly better than for the hitherto considered Higgs detection mode H --> Z Z* --> l+ l+ l- l-, where in this mass range about 100~fb-1 of integrated luminosity are required for a 5 sigma signal.

How to find a Higgs Boson with a Mass between 155--180 GeV at the LHC

TL;DR

This paper addresses the challenge of discovering a Standard Model Higgs boson in the mass range 155-180 GeV at the LHC, where decays to on-shell W pairs dominate but produce no sharp mass peak. The authors advocate using the fully leptonic decay H->W+W-->(l nu)(l' nu) as a discovery channel, including tau decays, and simulate signal and backgrounds with PYTHIA to account for hadronization and detector-level effects. They develop a sequence of cuts that exploit kinematic features and spin correlations of Higgs decays (e.g., dilepton opening angles, cos theta* distribution, jet veto, MET, and WW mass estimates) to suppress irreducible WW and ttbar backgrounds. They show that a signal-to-background ratio near unity and a discovery significance of 5-10 sigma can be achieved with about 5 fb-1 of data at 14 TeV, outperforming the ZZ*->4l channel in this mass window. These results suggest a fast, robust Higgs discovery path for ATLAS/CMS in this challenging mass window.

Abstract

We reconsider the signature of events with two charged leptons and missing energy as a signal for the detection of the Standard Model Higgs boson in the mass region M(Higgs)=155--180 GeV. It is shown that a few simple experimental criteria allow to distinguish events originating from the Higgs boson decaying to H --> W+W- from the non resonant production of W+W- X at the LHC. With this set of cuts, signal to background ratios of about one to one are obtained, allowing a 5--10 sigma detection with about 5~fb-1 of luminosity. This corresponds to less than one year of running at the initial lower luminosity L= 10**33/ cm**2/sec. This is significantly better than for the hitherto considered Higgs detection mode H --> Z Z* --> l+ l+ l- l-, where in this mass range about 100~fb-1 of integrated luminosity are required for a 5 sigma signal.

Paper Structure

This paper contains 4 sections, 4 equations, 4 figures, 2 tables.

Table of Contents

  1. Introduction
  2. $\mathbf { H\rightarrow W^{+}W^{-} \rightarrow (\ell^{+}\nu)(\ell^{'-}{\bar{\nu}})}$
  3. Selection Cuts
  4. Conclusions

Figures (4)

  • Figure 1: $| \cos \theta |$ distribution of the dilepton system with respect to the beam direction for Higgs signal and background events.
  • Figure 2: $\cos \phi$ distribution of the dilepton system in the plane transverse to the beam direction for Higgs signal and background events, cut number 6 has not yet been applied.
  • Figure 3: Estimated invariant mass of the $\ell \ell \nu \nu$ system for Higgs signal and background events.
  • Figure 4: $\cos \theta^{*}$ distribution in the dilepton rest frame for Higgs signal and background events.