Combined Upper Limit on Standard Model Higgs Boson Production at CDF for EPS 2011

The CDF Higgs Working Group


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Contents

Abstract
Documentation
(N)NLO Cross Section and Branching Ratio Table
Bayesian Framework
July 2011 Combined Results with up to 8.2 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 8.2 fb-1 of integrated luminosity is performed. For mH<125 GeV/c2, the sensitivity-weighted average luminosity for the contributing channels is 7.5 fb-1, and the main channels included for mH>150 GeV/c2 use a data sample corresponding to 8.2 fb-1. The channels considered are WH→ lνbb, VH→METbb, ZH→l-l+bb, H→γγ, VH→jjbb, H → W+W-, H→&tau-&tau++2jets, H→ZZ→llll, two searches for ttH production, and a search for associated production of WH or ZH with a tau and two leptons. 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 1.55 (1.49) and 0.75 (0.79) times the Standard Model production cross sections for Higgs boson masses of 115 and 165 GeV/c2, respectively. We exclude the ranges 156.5 < mH < 173.7 GeV/c2 and 100 < mH < 104.5 GeV/c2.

Documentation

Documentation for Each Channel


Cross Sections and Branching Ratios

We use the following references for our cross sections and branching ratios. The citations below include only those papers which contain numbers that we use. Further citations are available in our conference note.

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 up to 8.2 fb-1 (July 2011)

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 for the combination of all CDF Higgs search analyses. Limits are presented at the 95% CL. Limits for the H→bb channels. They are: lvbb, METbb, llbb, jjbb, and ttH. Limits are presented at the 95% CL.

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=100 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=100 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=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=150 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=150 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=165 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=165 GeV/c2
Background-subtracted data distributions for events in all channels, sorted and collected by s/b. The background is fit to the data. The error bars on the background-subtracted data points are the square roots of the best-fit background rates in those bins. The blue histograms show the remaining uncertainty on the background rates after the fit. The shaded histogram shows the expected signal yield for a 115 GeV/c2 Higgs boson. Background-subtracted data distributions for events in all channels, sorted and collected by s/b. The background is fit to the data. The error bars on the background-subtracted data points are the square roots of the best-fit background rates in those bins. The blue histograms show the remaining uncertainty on the background rates after the fit. The shaded histogram shows the expected signal yield for a 165 GeV/c2 Higgs boson.

Projections

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 luminosity for the July 2011 point is 5.6 fb-1, a sensitivity-weighted average of the contributing channels' analyzed luminosities. These plots are shown for mH=115 GeV/c2. 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. This plot is shown for mH=160 GeV/c2. The luminosity for the July 2011 point is 5.9 fb-1.

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

July 2011, CDF Higgs Discovery Group