Combined Tevatron upper limit on gg->H->W+W- and constraints on the Higgs boson mass in fourth-generation fermion models

Abstract

We combine results from searches by the CDF and D0 collaborations for a standard model Higgs boson (H) in the process gg->H->W+W- in p=pbar collisions at the Fermilab Tevatron Collider at sqrt{s}=1.96 TeV. With 4.8 fb-1 of integrated luminosity analyzed at CDF and 5.4 fb-1 at D0, the 95% Confidence Level upper limit on σ(gg->H) x B(H->W+W-) is 1.75 pb at m_H=120 GeV, 0.38 pb at m_H=165 GeV, and 0.83 pb at m_H=200 GeV. Assuming the presence of a fourth sequential generation of fermions with large masses, we exclude at the 95% Confidence Level a standard-model-like Higgs boson with a mass between 131 and 204 GeV.

Figures (4)

• Figure 1: Distributions of the neural network outputs for the search for a Higgs boson of mass $m_H=200$ GeV, from CDF. The data are shown as points with uncertainty bars, and the background predictions are shown stacked. The figures show the distributions for events with (a) zero, (b) one, and (c) two or more identified jets, respectively. The distributions are summed over lepton categories. The fourth-generation signal, normalized to the prediction of the low-mass scenario, is shown not stacked.
• Figure 2: Distributions of the neural network outputs for the search for a Higgs boson of mass $m_H=200$ GeV, from D0 summed over all jet multiplicities. (a) shows the distribution for the di-electron selection, (b) shows the distribution for the electron-muon selection, and (c) shows the distribution for the di-muon selection. The data are shown as points with uncertainty bars, and the background predictions are shown stacked. The background uncertainty is the post-fit systematic uncertainty. The fourth-generation signal, normalized to the prediction of the low-mass scenario, is shown not stacked.
• Figure 3: Background-subtracted data distribution for the discriminant histograms, summed for bins of $s/b$, for the $m_H$ = 200 GeV combined search. The background is fitted to the data under the background-only hypothesis, and the uncertainty on the background is the post-fit systematic uncertainty. The signal, which is normalized to the low-mass fourth-generation SM expectation, is shown with a filled histogram. The uncertainties shown on the background-subtracted data points are the square roots of the post-fit background predictions in each bin, representing the expected statistical uncertainty on the data.
• Figure 4: The CDF, D0, and combined observed (solid black lines) and median expected (dashed black lines) 95% C.L. upper limits on $\sigma(gg\rightarrow H)\times \mathcal{B}(H\rightarrow W^+W^-)$ are shown in figures (a) through (c). The shaded bands indicate the $\pm 1$ standard deviation (s.d.) and $\pm 2$ s.d. intervals on the distribution of the limits that are expected if a Higgs boson signal is not present. Also shown on each graph is the prediction for a fourth-generation model in the low-mass and high-mass scenarios, 4G (Low mass) and 4G (High mass) respectively. The hatched areas indicate the theoretical uncertainty from PDF and scale uncertainties. The lighter curves show the high-mass theoretical prediction. Figure (d) shows the 95% C.L. combined limit relative to the low-mass theoretical prediction, where the uncertainties in the signal prediction are included in the limit. Also shown in Figure (d) is the prediction of the signal rate in the high-mass scenario, divided by that of the low-mass scenario.