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Wtop 1lepton background in SUSY CSC Notes 12 ATLAS SUSY WG

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Need to estimate background for SUSY from data ... Estimated BG overestimated by factor 2 !!! WHY? SUSY in control region. Method-1 2D (NIKHEF) ... – PowerPoint PPT presentation

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Title: Wtop 1lepton background in SUSY CSC Notes 12 ATLAS SUSY WG


1
W/top 1-lepton background in SUSYCSC Notes 1/2
ATLAS SUSY WG
  • A. Koutsman W. Verkerke
  • 01-03-2007

2
Main Idea
  • Need to estimate background for SUSY from data
  • For 1-lepton mode ttbar and Wjets dominant
    background processes
  • DATA a Top ß W d SUSY
  • HOW DO WE GET a, ß, d?

3
Samples
  • W0,1,2,3,4,5 partons (Alpgen)
  • WenunJets (n2..5) 5223-5226 WmununJets
    (n3..5) 8203-8205 WtaununJets
    (n2..5) 8208-8211
  • added with the right luminosities
  • T1 (MC_at_NLO) 5200
  • separate at truth-level between
  • semi-leptonic e, mu, tau
  • SU3 (Jimmy) 5403
  • All samples normalized to 100 pb-1
  • All following plots for ELECTRONS

4
Method-1
  • Idea get control sample with Mtlt100 and
    extrapolate to region with Mtgt100
  • Extrapolation Scale by events missing-Et
    100-200 GeV range
  • Look at distributions of missing-Et, effective
    mass, pt leading jet

5
Results Method-1
  • First try-out with Top Wnjets samples
  • Results look good!!!
  • Actual BG can be estimated correctly

6
Results Method 1
  • Now with Top Wnjets SUSY samples
  • Estimated BG overestimated by factor 2 !!!

WHY?
SUSY in control region
7
Method-1 2D (NIKHEF)
  • Lets look at 2D distribution missing-Et vs. Mt
  • Find a region which is SUSY-free
  • Extrapolate

8
Method-1 2D (NIKHEF)
  • No clear SUSY free region
  • Make a 2D-fit for each distribution

9
Results Method-1 2D (NIKHEF)
  • Divide Mt in 10 equal parts and look at
    missing-Et distributions
  • TTbar and WJets distributions resemble ee

TTbar
WJets
SUSY
10
Results Method-1 2D (NIKHEF)
  • Fit an exponential to each projection
  • Plot slope for all projections

WJets Projection 35ltMtlt65
TTbar
WJets
11
Results Method-1 2D (NIKHEF)
  • PDFs are factorizable
  • Very simple extrapolation

TTbar
WJets
12
What about SUSY?
  • Still in the control region
  • SUSY distribution is flat for missing-Etlt200 and
    in Mtlt200
  • Do the fit of a model with 3 components and
    extrapolate (work in progress)
  • Check stability of procedure

13
Future Plans
  • Do the fit and check stability
  • Do the same for other SUSY points
  • With another variable than Mt, try to find a
    SUSY-free region (tried with Meff,
    Mtop(hadronic), Ht(sum pt jetsleptons) without
    succes)
  • Try different method SUSY free region by
    requiring 2 jets and extrapolating to 4
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