Search for a Standard Model Higgs boson in the decay channel H to ZZ to 2l2tau

Abstract

A search for the standard model Higgs boson in the decay mode $ H \to ZZ \to 2l2\tau$, where $l = {\mu, e}$ is presented based on CMS data corresponding to an integrated luminosity of 1.1 fb$^{-1}$ at $\sqrt{s}=7$ TeV. No evidence is found for a significant deviation from standard model expectations anywhere in the ZZ mass range considered in this analysis. An upper limit at 95\% C.L. is placed on the product of the cross-section and decay branching ratio for the Higgs boson decaying with standard model-like couplings, which excludes cross-sections of about ten times the expected value for Higgs boson masses in the range $200 < m_{\rm H} < 400 \, \rm{GeV/c^2}$.

Main Results

In $1.1 \fbinv$ of data one event isobserved in the 8 search channels, in the $eee\tau$ state, as compared to 2.5 background events expected. The reconstructed $2l2\tau$ invariant mass for all decay channels is presented i n Fig.~\ref{figure:invmass}. The stacked background shapes are simulated using MC and normalized to the values obtained using the method outlined above. The expected mass distributions for the SM Higgs with masses $m_{\rm H} = 200$ and $m_{\rm H} = 400 \, \rm{GeV/c^2}$ are also shown. No evidence is found for a significant deviation from standard model expectations anywhere in the $ZZ$ mass range considered in this analysis. The total signal acceptance, which also includes the branching ratios of individual tau channels, varies between 0.01--0.02 for a Higgs mass of 200 GeV and various tau decay channels and increases by factor of three to four towards 450 GeV. This is expected since the final-state leptons produced in tau decays are softer than those from direct $Z \to ll$ production and the selection requirements and lepton reconstruction become more efficient at high Higgs masses.

Expected and observed 95\% C.L. (confidence level) upper limits are set on the cross-section ratio to the nominal SM Higgs cross-section using the modified frequentist construction CL$_{\rm{s}}$~\cite{CLS1, CLS2}. They are presented as a function of the Higgs mass in Fig.~\ref{figure:limitPlot}. The bands represent the $1 \sigma$ and $2 \sigma$ probability intervals around the expected limit. The upper limit on the cross-section is approximately ten times the SM cross-section in the range of $200 < m_{\rm H} < 400 \, \rm{GeV/c^2}$.

Figures from HIG-11-013

Figure	Label	Description
	pdf	The expected and observed 95\% C.L. upper limits on the product of the production cross-section and decay branching ratio for a Higgs boson normalized to the SM expectation as a function of $m_{\rm H}$. At $m_{\rm H} = 180\, \rm{GeV/c^2} $ the less restrictive limit is due to the rapidly decreasing branching ratio of $H \to ZZ$ in the SM. The one- and two-standard-deviation ranges are also shown.

pdf

The four-lepton reconstructed mass summed for all $2l2\tau$ final states. The data corresponds to an integrated luminosity of 1.1 \fbinv. The stacked background shapes are the result of a MC simulation and normalized to the values obtained using the data--driven techniques explained in the text. The expected mass distributions for the SM Higgs boson with a mass 200 or 400 GeV are also shown.

pdf

Comparison between data and simulation for the background estimation in same-sign, anti-isolated control region for $\mu \mu \tau \tau$ (left plot) events.

pdf

Comparison between data and simulation for the background estimation in same-sign, anti-isolated control region for $ee \tau \tau$ (right plot) events.

-- AlexanderSavin - 21-Aug-2011