Combined Upper Limit on Standard Model Higgs Boson Production at CDF for HCP 2009

The CDF Higgs Working Group


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Contents

Abstract
Documentation
(N)NLO Cross Section Table
Bayesian Framework
Posterior Probability
Expected limits from Pseudo Experiments
November 2009 Combined Results with 4.8 fb-1
Summary Plots sorted by s/b
Projections
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Abstract

A combination of several searches for Standard Model Higgs boson production at CDF using a data sample up to 4.8 fb-1 of integrated luminosity is performed. The channels considered are WH→ lνbb, VH→METbb, ZH→l-l+bb, gg → H → W+W-, and a search H→&tau-&tau++2jets. We calculate combined upper limits on the ratio of the Higgs boson cross section times the branching ratio to its Standard Model prediction (R95) for Higgs boson masses between 100 and 200 GeV/c2. The results are in good agreement with the expectations obtained from background-only pseudo-experiments. The 95% CL upper limits observed (expected) are factors of 3.12 (2.38) and 1.18 (1.19) higher than the Standard Model production cross sections for Higgs boson masses of 115 and 165 GeV/c2, respectively.

Documentation

Documentation for Each Channel


Cross Sections

Cross Sections are obtained from TeV4LHC Higgs working group, with the following modifications: The branching ratios are obtained from John Conway's Calculation with HDECAY

Bayesian Framework


The integrals over the uncertain parameters with their correlated priors from external constraints are done with a Markov Chain Monte Carlo integration method, using the Metropolis-Hastings algorithm.

Combination Results with 4.8 fb-1 (November 2009)

The combined upper limit as a function of the Higgs boson mass between 100 and 200 GeV/c2 Solid black: observed limit/SM; Dashed black: median expected limit/SM. Colored bands: +-1, 2 sigma distributions around median expected limit. The combined upper limit as a function of the Higgs boson mass between 100 and 200 GeV/c2. Solid lines indicate the observed upper limit for each channel and combined result (dark red). Dashed lines indicate the median expected upper limit for each channel and the combined result (dark red).
 
The summary table of observed and expected limits between 100 and 200 GeV/c2.

Posterior Probability

Posterior densities for all channels combined for Higgs boson mass between 100 and 200 GeV/c2.

Expected Limits with Pseudo-experiments

Limits are computed with simulated data sets drawn from systematically varied template histograms. The observed limits are indicated with red vertical lines. The median expected limits in the absence of a Higgs boson signal are shown with dashed vertical lines. 68% of limits are expected to fall within the green shaded area, and 95% of limits are expected to fall within the top and bottom of the yellow-shaded areas, again assuming no signal is truly present.


Events Ranked by s/b

Events in all search channels, sorted by the s/b in the bins in which they are found. Signal and background totals are shown, stacked. This plot is shown for mH=115 GeV/c2 Cumulative distributions of background, data and signal+background. The s/b distribution is integrated from the high s/b side downwards. This plot is shown for mH=115 GeV/c2
Events in all search channels, sorted by the s/b in the bins in which they are found. Signal and background totals are shown, stacked. This plot is shown for mH=160 GeV/c2 Cumulative distributions of background, data and signal+background. The s/b distribution is integrated from the high s/b side downwards. This plot is shown for mH=160 GeV/c2

Projections

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Achieved and projected median expected upper limits on the SM Higgs boson cross section, by date. The solid lines are 1/sqrt(L) projections. The top of the orange band corresponds to the Summer 2007 performance expected limit divided by 1.5, and the bottom of the orange band corresponds to the Summer 2007 performance expected limit divided by 2.25. The bottom plot is the same as the top plot but has a logarithmic scale for the expected limit. The Luminosity used for the November 2009 point is (2*Llvbb+2*LMETbb+Lllbb+0.5*LHττ+0.5*Ljjbb)/6 = 3.65 fb-1, an approximation to how much the channels contribute per unit luminosity. These plots are shown for mH=115 GeV/c2Achieved and projected median expected upper limits on the SM Higgs boson cross section, by date. The solid lines are 1/sqrt(L) projections. The top of the orange band corresponds to the Summer 2007 performance expected limit divided by 1.5, and the bottom of the orange band corresponds to the Summer 2007 performance expected limit divided by 2.25. The bottom plot is the same as the top plot but has a logarithmic scale for the expected limit. The luminosity used for the November 2009 point is the 4.8 fb-1 of the H→WW analyses. These plots are shown for mH=160 GeV/c2

2xCDF Projections

For current D0 Higgs Search Results and Performance, please visit D0's Higgs Results Web Page.

Projected median expected upper limits on the SM Higgs boson cross section, scaling CDF performance to twice the luminosity. The solid lines are 1/sqrt(L) projections, as functions of integrated luminosity per experiment. The top of the orange band corresponds to the Summer 2007 performance expected limit divided by 1.5, and the bottom of the orange band corresponds to the Summer 2007 performance expected limit divided by 2.25. This plot is shown for mH=115 GeV/c2 Projected median expected upper limits on the SM Higgs boson cross section, scaling CDF performance to twice the luminosity. The solid lines are 1/sqrt(L) projections, as functions of integrated luminosity per experiment. The top of the orange band corresponds to the Summer 2007 performance expected limit divided by 1.5, and the bottom of the orange band corresponds to the Summer 2007 performance expected limit divided by 2.25. This plot is shown for mH=160 GeV/c2
Probability of seeing a 2σ excess as a function of mH for analyzed integrated luminosities of 5 fb-1 and 10 fb-1 per experiment, assuming CDF and D0 perform the same. Two scenarios are shown, in which channels have the same performance as for the Winter 2009 combination (solid lines), and for the case with another factor of 1.5 in the sensitivity (dashed lines). The current observations are not taken into account, only expected sensitivities are shown. Sensitivities are expected to scale with sqrt(L). Probability of seeing a 3σ excess as a function of mH for analyzed integrated luminosities of 5 fb-1 and 10 fb-1 per experiment, assuming CDF and D0 perform the same. Two scenarios are shown, in which channels have the same performance as for the Winter 2009 combination (solid lines), and for the case with another factor of 1.5 in the sensitivity (dashed lines). The current observations are not taken into account, only expected sensitivities are shown. Sensitivities are expected to scale with sqrt(L).


Experimental Contacts

If you wish to present this material publicly or would like further information, please email the CDF combination group and conveners

Doug Benjamin    dbenjamin  AT fnal.gov
Matt Herndon     herndon    AT hep.wisc.edu
Eric James       jameseb    AT fnal.gov
Tom Junk         trj        AT fnal.gov
Ben Kilminster   bjk        AT fnal.gov
Nils Krumnack    nils       AT fnal.gov
Weiming Yao      wmyao      AT lbl.gov

November 17, 2009 CDF Higgs Working Group