CDF Logo Search for a SM Higgs Boson with the Diphoton Final State at CDF using 7.0fb-1 of Data

 

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Introduction

The first SM result in this channel by CDF was obtained using 5.4fb-1 of data with "central" photons (|&eta|<1.1) selected using standard CDF photon ID. The current result increases sensitivity with 7.0 fb-1 of data and the addition of three improvements: (a) reducing backgrounds for regular central photons using a neural network (NN) discriminator, (b) including "plug" photons (1.2<|&eta|<2.8), and (c) reconstructing central photons that convert into an electron-positron pair. The use of the latter two improvements allows for three new channels to be added: a central-plug (CP) category where two regular photons are found, one in the central region and one in the plug region; a central-central conversion category (CC conversion) where a regular central photon and a central conversion photon are identified; and a central-plug conversion category (CP conversion) where one regular plug photon and a central conversion photon are found. The first improvement, using a NN to identify central photons, most significantly enhances the CC channel where two central photons are selected, but additionally benefits the CP and CC conversions categories which also include central photons.

Simulation of Higgs Boson Diphoton Mass Spectrum

For each channel, simulation of the diphoton mass spectrum for a Higgs boson with a mass of 120 GeV/c2 decaying into two photons. The mass resolution of the diphoton channel is extremely good compared to dijet decay modes (Gaussian sigma / mean < 3%).


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Signal Acceptance


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Data-Driven Background Model

The invariant mass distribution is used as a discriminant for separating Higgs signal from the background. No significant narrow resonance is observed in the data. A smooth fit is made to the diphoton invariant mass distribution of the data using sidebands for each Higgs test mass and then interpolating to the signal region of that test mass. A Breit-Wigner function is added to the CP channels in order to model the Z boson contribution. The fit in the signal region is used to establish the background expectation. Example fits below are made from a Higgs test mass window of 120 GeV/c2 with the corresponding data vs. fit residual also shown.


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Expected and Observed Limits Relative to Standard Model Prediction

95% C.L. upper limits are set on the production cross section times branching fraction relative to the standard model prediction using a Bayesian binned likelihood approach.

 
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Additional plots

 

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  Paged prepared by Karen Bland
For problems or questions regarding this website contact kbland@fnal.gov
Last updated: 04/18/11