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