ATLAS: Missing Transverse Energy in the Search for Supersymmetry
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ATLAS: Missing Transverse Energy in the Search for SupersymmetryChristine McLeanThe College of William and MaryUniversity of Michigan REUAdvisor: Dr. Richard TeuscherAugust 11, 2011
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ATLAS – A Toroidal LHC ApparatuS•Multipurpose LHC Detector
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The Search for Supersymmetry - SUSY•Solve Standard Model Problems
▫ Hierarchy Problem What keeps the Higgs Mass from Blowing
Up? 100 GeV [Electroweak] vs. 10^19 GeV
[Gravity]•Sparticles – Supersymmetric Partner
Particles•Favored Model: mSUGRA
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Goal: Supersymmetry Detection•Found from
missing transverse energy in the detector
•MET left by SM background and neutralinos
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Missing ET – SM Background•W+Jets
•Z+Jets
•QCD jet (mismeasurement)
•T Tbar
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Early Plots – Jet Sample
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Monte Carlo Plots – Background and Signal
Jet Pileup Bug
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Cuts for Signal Region A•Different cuts on
the data for different SUSY production processes
•Focused on signal region A: light-˜q˜q production
• Source: ▫ Search for squarks and gluinos using final
states with jets and missing transverse momentum with the ATLAS detector in sqrt(s) = 7 TeV proton-proton collisions
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Important Cuts – Delta Phi and Effective Mass (Meff)•Meff = Jet Pt + MET; Meff >500 GeV•Delta Phi Absolute Value> 0.4
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Plots after Meff Cut
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Plots After Last Official Cut
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One Additional MET Cut – MET > 225 GeV
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Data and Future•Full Monte Carlo
Analysis Can be used to Compare to LHC Data
•Z->ee Data to Look for SUSY in Two Lepton Mode▫MC needs to be
scaled to Data Luminosity First
ATLAS Work in
Progress
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Travels and Food
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Acknowledgements•REU Leaders: Homer Neal, Steve
Goldfarb, Jean Krisch, Junjie Zhu, and Lauren Rugani
•Advisor: Richard Teuscher•ATLAS Canada Graduate Students: Travis
Bain, Nikolina Ilic, and Reyhaneh Rezvani•Fellow REU and CERN summer students•NSF and CERN
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Hierarchy Problem - Backup
Source: Travis Bain
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Hierarchy Problem - Backup
Source: Travis Bain
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Supersymmetry Unification - Backup
Source: Travis Bain
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Monte Carlo - Backup•Event Generator– generates random
numbers and decides whether event happens based on probability▫ATLAS – after generating events, showers
them through the detector to get a readout simulation
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SM Missing ET Background and Cuts- Backup
Source: Nikolina Ilic
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Cut Flow Table - Backup