Signal and Background Modeling for H → 4l

Peter Vankov

UK Higgs Meeting, RAL 17.07.2008

17.07.2008 Peter Vankov 2/13

Study of the Signal and Background shapes in Higgs → 4l (2µ2e, 4µ, 4e)

Define a model (PDF)

Extract the parameters of the model

Extract the Higgs signal significance

Overview

Goal:

Signal: So far - Heavy Higgs, M=300 GeV

Background: ZZ → 4l

Analysis tools:

- Athena, 13.0.30 - HiggsToFourLeptons package - Standard CSC selection

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RooFit

What is it?

• A powerful toolkit for modeling the expected distribution(s) of events in a physics analysis

• Primarily targeted to high-energy physicists using ROOT

• Originally developed for the BaBar collaboration by Wouter Verkerke and David Kirkby.

• Included with ROOT v5.xx

Documentation:

• http://root.cern.ch/root/Reference.html – for latest class descriptions. RooFit classes start with “Roo”.

• http://roofit.sourceforge.net – for documentation and tutorials

Statistical tool

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Choosing models

SignalPDF(Sig): Breit-Wigner PDF(Sig): Bifurcated Gaussian

Background

PDF(Bkg): Exponential function

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Applying the chosen models

H(300 GeV)

30/fb

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Total PDF(Signal+Background) = PDF(Bkg) * (1-SB_frac) + SB_frac * PDF(Sig)

30/fb

Creating a total (Sig+Bkg) model

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Toy MC experiments

Performing 200 Toy MC experiments

Model 1 Model 2

Using RooMCStudy

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Sensitivity to model parameters

Model 1

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Sensitivity to model parameters

Model 1

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Sensitivity to model parameters

Model 2

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Sensitivity to model parameters

Model 2

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Signal Significance

Model 1 Model 2

CSC note (7 june’2008): σ = 13.8

H(300 GeV)

30/fb

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Work in progress

Looking at other Higgs masses

Experiment with other models

Use custom analysis (alternative to HiggsToFourLeptons)

Gauss + Landau BiFurGauss + Landau

Summary and To Do