Search for SUSY in Events with Taus , Jets, and MET

1. Jieun Kim ( CMS Collaboration ) APCTP 2012LHC Physics Workshop at Korea (Aug. 7-9, 2012) Search for SUSY in Events with Taus, Jets, and MET

2. Contents • Theoretical Motivation • Search Strategy • Event Selections • Backgrounds • Sensitivity for SUSY models • Summary

3. SUSY Dark Matter • Supersymmetrized Standard Model between Fermions and Bosons with unification of gauge couplings • Supergravity (mSUGRA or CMSSM) models, • the lightest neutralino is the stable LSP which escapes the detector • Cosmologically a natural dark matter (DM) candidate • ( stable neutralino ) • stau-neutralino co-annihilation processes may be sensitive to the amount of dark matter relic density observed by the Wilkinson Microwave Anisotropy Probe (WMAP)

4. SUSY Signature • SUSY signature at the LHC is involved with high multiplicity of energetic jets because squark and gluino pairs are dominant at the pp collisions, a large momentum imbalance in the detector (from LSP CDM candidate), and the Taus in the stau-neutralino co-annihilation region

5. SUSYSearch @ LHC Dark Matter Identity In large tan beta, Branch ratio to taus becoming dominant ~100%

6. pp@√s = 7TeV, 4.98 fb-1of data Particle Flow Jets clustered from identified particles reconstructed using all detector components with Anti-Kt (R=0.5) jet clustering algorithms • HT = scalar sum of Jet pT • MHT = negative vector sum of Jet pT

7. Tau lepton Reconstruction and Identification • Electromagnetic strips with ET>1 GeVfor 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% μ Pt = 23.1 GeV/c η = -1.31 Z → ττ→ μ + τh (one prong tau) τ Pt = 36.8 GeV/c η = 0.03 7

8. Event Selections MHT 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 thth pair with ΔR(τh,1, τh,2) > 0.3 • Δφ(j2, MHT) > 0.5 pT(j1) pT(j2)

9. Backgrounds

10. 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 mistagrates 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 taus Correction factor

11. Background Control Samples

12. TTbar Two types of events in TTbar control region: • 1 real τh + 1 jet faking a τ • 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. • ετiso =Tau isolation efficiency. • C(N,n) = N choose n.

13. WJets Two types of events in W+Jets control region: • 1 real τh + 1 jet faking a τ. • 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. • ετiso =Tau isolation efficiency. • C(N,n) = N choose n.

14. Invisible Z + Jets • Aμ= μ acceptance efficiency. • ɛμ = μ ID efficiency. • B(Z νν) = branching ratio for Z νν • B(Zμμ) = branching ratio for Z  μμ • ɛTriggerMHT= efficiency of HLT_PFMHT150 (plateau) • εTriggerμτ = 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.

15. Z->tau tau + Jets • Aμ= μ acceptance efficiency. • ɛμ = μ ID efficiency. • B(Z νν) = branching ratio for Z νν • B(Zμμ) = branching ratio for Z  μμ • B(τ  τh) = branching ratio for hadronicτ decay • ɛTriggerMHT= efficiency of HLT_PFMHT150 (plateau) • εTriggerμτ = 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.

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

17. Search for New Physics

18. The Highest HT Event

20. Sensitivity in SUSY models • Supergravity models (mSUGRA/CMSSM) • Simplified Model Scenarios (SMS) • Gauge Mediated Supersymmetry Breaking Models (GMSB)

21. CMSSM / mSUGRA • 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.

22. CMSSM / mSUGRA • 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 effectively detected and only the energetic tau from the decay of the neutralino can be observed

23. SMS Gluino mass < 775 GeV@95% C.L. for LSP mass up to 325 GeV

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

25. Summary • SUSY (R-parity conserved) search results with up to ~5/fbof 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 ~TeVwith the 2011 data of pp@√s = 7TeV

26. Systematic Uncertainty

27. The Highest HT Event