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Search for SUSY in Events with Taus,

Jets, and METJieun Kim

( CMS Collaboration )

APCTP 2012 LHC Physics Workshop at Korea(Aug. 7-9, 2012)

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ContentsTheoretical MotivationSearch StrategyEvent SelectionsBackgroundsSensitivity for SUSY modelsSummary

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Supersymmetrized Standard Model between Fermions and Bosons with unification of gauge couplings

SUSY Dark Matter

Cosmologically a natural dark matter (DM) candidate ( stable neutralino )

Supergravity (mSUGRA or CMSSM) models, the lightest neutralino is the stable LSP which es-capes the detector 0

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stau-neutralino co-annihilation processes may be sensitive to the amount of dark matter relic density observed by the Wilkinson Microwave Anisotropy Probe (WMAP)

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SUSY signature at the LHC is involved with high multiplicity of energetic jets be-cause squark and gluino pairs are dom-inant at the pp colli-sions, a large momen-tum imbalance in the detector (from LSP CDM candidate), and the Taus in the stau-neutralino co-annihi-lation region

SUSY Sig-nature

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SUSY Search @ LHCDark Matter Identity

In large tan beta, Branch ratio to taus becoming dominant ~100%

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pp@√s = 7TeV, 4.98 fb-1 of data

Particle Flow Jets clustered from identi-fied particles reconstructed using all detector components with Anti-Kt (R=0.5) jet clustering algorithmsHT = scalar sum of Jet pT MHT = negative vector sum of Jet pT

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Tau lepton Reconstruction and Identification

Electromagnetic strips with ET>1 GeV for neutral pions combined with PFJets to reconstruct the tau decay modes

Isolation: no charged hadrons with PT > 1.5 GeV/c or photons with ET > 2.0 GeV in Δ R < 0.3

Muon ID efficiency 72.8%, tau ID efficiency 64.1%

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Single Hadron + Zero StripsSingle Hadron + One (two) Strip

Single Hadron + Two StripsThree Hadronsρ(770)

Z → τ τ → μ + τh (one prong tau)

μ Pt = 23.1 GeV/cη = -1.31

τ Pt = 36.8 GeV/cη = 0.03

Event Selections

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Baseline Selections: 2 Jets + MHT• ≥1 PFJet with pT > 30 GeV/c• 1st Leading Jet pT > 100 GeV/c and |η| < 3• 2nd Leading Jet pT > 100 GeV/c and |η| < 3• MHT > 250 GeV (with plateau “HLT_PFMHT150”)

Tau Selections: 2τh

• ≥ 2 τh’s with pT > 15 GeV/c and |η| < 2.1• ≥ 2 τh’s passing the HPS ”tight” μ veto• ≥ 2 τh’s passing the HPS ”tight” e veto• ≥ 2 τh’s passing the HPS decay mode finding• ≥ 2 τh‘s passing the HPS ”very loose” isolation

Topological Selections:• 1st Leading Jet separated from th’s (ΔR(j1, τh) > 0.3)• 2nd Leading Jet separated from th’s (ΔR(j2, τ) > 0.3)• ≥ 1 th th pair with ΔR(τh,1, τh,2) > 0.3• Δφ(j2, MHT) > 0.5

MHT

pT(j1)

pT(j2)

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Backgrounds

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Background Estimation in data driven

Define control samples which are selected with most of the selections similar to those used in the main search but enriched with events from the background process

Measure selection efficiencies of jet->tau mistag rates in those control regions

Extrapolate to the region where we expect to observe our signal.

Estimate following equation for each background (ttbar, wjets, zjets, but except QCD) contribution

Probability of (0,1,2) jets faking tausCorrection factor

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Background Control Samples

TTbar

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Two types of events in TTbar control region:1. 1 real τh + 1 jet faking a τ2. 2 jets faking 2 τ.

• Aτ+j = fraction of t-tbar events with 1 real τh and 1 jet. • Aj+j = fraction of t-tbar events with 2 jets.• P(N) & P(M) are the probabilities to have N (M) jets that can fake the τ in category (1) and (2). • f = “fake rate” • P(2b) = Probability of tagging 2-b-jets.• ετ

iso =Tau isolation efficiency. • C(N,n) = N choose n.

WJets

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Two types of events in W+Jets control region:1. 1 real τh + 1 jet faking a τ.2. 2 jets faking 2 taus.

• Aτ+j = fraction of Wjet events with 1 real τh and 1 jet faking τ• Aj+j = fraction of Wjet events with 2 jets faking τ’s• P(N) & P(M) are the probabilities to have N (M) jets that can fake the τ in category (1) and (2)• f = “fake rate” • P(0b) = Probability of tagging zero jets as b-jets.• ετ

iso =Tau isolation efficiency. • C(N,n) = N choose n.

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Invisible Z + Jets

• Aμ = μ acceptance efficiency.• ɛμ = μ ID efficiency.• B(Z νν) = branching ratio for Z νν• B(Zμμ) = branching ratio for Z μμ• ɛTrigger

MHT = efficiency of HLT_PFMHT150 (plateau)• εTrigger

μτ = efficiency of μτ cross-trigger.• ɛMHT = efficiency of MHT (>250)• P(N) is the probability to have N jets that can fake the τ in category (1) and (2). • f = “fake rate” • C(N,n) = N choose n.

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• Aμ = μ acceptance efficiency.• ɛμ = μ ID efficiency.• B(Z νν) = branching ratio for Z νν• B(Zμμ) = branching ratio for Z μμ• B(τ τh) = branching ratio for hadronic τ decay• ɛTrigger

MHT = efficiency of HLT_PFMHT150 (plateau)• εTrigger

μτ = efficiency of μτ cross-trigger.• ɛMHT = efficiency of MHT (>250)• P(N) & P(M) are the probabilities to have N (or M) jets that can fake τ• f = “fake rate” • C(N,n) = N choose n.

Z->tau tau + Jets

QCD multijets

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For QCD contribution, obtain a data-MC scale factor (SFQCD)

Search for New Physics

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)540(1J

)424(2J

)21(2

)117(1

)72(3J

)68(4J

)540(1J

)424(2J

)72(3J

)68(4J)117(1

The Highest HT Event

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Sensitivity in SUSY models

Supergravity models (mSUGRA/CMSSM)

Simplified Model Scenarios (SMS)

Gauge Mediated Supersymmetry Breaking Models (GMSB)

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• tanβ = 40, Ao = 500 GeV, μ > 0, Mtop = 173.8 GeV • Gaugino mass of < 495 GeV @ 95% C.L.• Gluino mass < 1.15 TeV @ 95% C.L.

CMSSM / mSUGRA

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With Single Tau : Better sensitivity in the case of very small ∆M (~5GeV) in the co-annihilation region, the low energy tau can’t be ef -fectively detected and only the energetic tau from the decay of the neutralino can be observed

CMSSM / mSUGRA

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SMSGluino mass < 775 GeV @ 95% C.L. for LSP mass up to 325 GeV

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GMSB

Gluino mass < 900 GeV @ 95% C.L.

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Summary SUSY (R-parity conserved) search results with up to

~5/fb of data, observed no significant excess.

SM background estimations done with data driven methods.

Setting the 95% exclusion limits on the constrained MSSM models, SUSY Simplified model, and GMSB.

Limits on Gluino mass reach to ~TeV with the 2011 data of pp@√s = 7TeV

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Systematic Uncer-tainty

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The Highest HT Event