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Trileptons @ CDF

Trileptons @ CDF. Melisa Rossi -- Udine University On behalf of the Multilepton Group CDF Collaboration Meeting Elba, June 2-10, 2006. Contents. Supersymmetry introduction The trilepton signature CDF search for chargino and neutralino Analysis approach Results

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Trileptons @ CDF

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  1. Trileptons @ CDF Melisa Rossi -- Udine University On behalf of the Multilepton Group CDF Collaboration Meeting Elba, June 2-10, 2006 Collaboration Meeting

  2. Contents • Supersymmetry introduction • The trilepton signature • CDF search for chargino and neutralino • Analysis approach • Results • CDF Run II Limit on chargino mass • Conclusions and outlook Collaboration Meeting

  3. Supersymmetry • No evidence of SUSY yet • must be a broken symmetry • Extends the Standard Model (SM) by adding a new spin symmetry • boson ↔ fermion • SUSY more than doubles SM particle spectrum • SUSY naturally solves open SM issues providing • stabilization of EWK scale • a framework for unification of forces • a dark matter candidate Collaboration Meeting

  4. Supersymmetry • SUSY breaking mechanism • determines phenomenology • determines search strategy at colliders • mSUGRA is our benchmark model • only 5 free parameters • R-parity • additional quantum number • Rp = (-1) 3(B-L)+2s • Rp conservation leads to • SUSY particles are pair produced • lightest super particle (LSP) stable m0: common scalar mass at GUT scale m1/2: common gaugino mass at GUT scale tan β: ratio of Higgs vacuum expectation values A0: trilinear coupling Sign(μ): sign of Higgs mass term Collaboration Meeting

  5. SUSY cross sections are small! Tevatron Cross sections (pb) 100 events per fb-1 Concentrating on chargino and neutralino m (GeV) Collaboration Meeting

  6. +interfering t-channel squark exchange diagrams Chargino & Neutralino • Mixture of SUSY partners of W, Z, photon, Higgs • Production & Decay FINAL STATE 3 isolated leptons + missing energy Tevatron GOLDEN signature Collaboration Meeting

  7. Analysis approach The “signal” region is investigated in data only at the very end of the analysis Kinematic regions where New Physics expected to be small LOOK in the SIGNAL REGION and compare the number of predicted events to the number of observed events Collaboration Meeting

  8. Collaboration Meeting

  9. Leading lepton Next-to-leading lepton Third lepton I. Analyses @ CDF • Many analyses to maximize the acceptance • 3 leptons • 2 leptons + track • 2 leptons with like sign (LS) Leading lepton pT > 20 GeV/c Leading lepton pT > 10 GeV/c Collaboration Meeting

  10. II. SM Backgrounds • Drell-Yan production + additional lepton • Leptons cover a wide range in pT • Small missing transverse energy • Low jet activity • Heavy flavour production • Leptons have mainly low pT • Leptons are rarely isolated • Missing transverse energy due to neutrinos • Diboson (WZ,ZZ) production • Leptons have high pT • Leptons are isolated • Missing transverse energy due to neutrinos Irreducible Collaboration Meeting

  11. Electron Fake rate per Jet Jet ET II. Other Backgrounds • Additional lepton contribution in the event comes from • Fake leptons • Fake rates extracted from Inclusive Jet Sample with different trigger thresolds • Conversion electrons • Probability of identifying conversion electrons measured • once the standard CDF removal algorithm is applied • based on calorimeter information Collaboration Meeting

  12. III. Basic Analysis Selection • Two lepton preselection • leading lepton pT>20 (15-5) GeV/c • next-to leading pT>10 (8-5) GeV/c • Invariant Mass • remove J/ψ,Υ, Z resonances •  • reject Drell-Yan and cosmics • Jet activity • reject ttbar, W+jets, Z+jets • Missing Transverse Energy • further Drell-Yan rejection Collaboration Meeting

  13. Invariant Mass Distributions Two lepton preselection Asking three leptons Dimuon Mass Removing resonanses by • Mll < 76 & Mll > 106 GeV/c2 • Mll > 15 (20, 25) GeV/c2 • min Mll < 60 GeV/c2 (dielectron+track analysis) Dimuon Mass Collaboration Meeting

  14.  & low jet activity Number of jets Dielectron  Low jet activity • Njets < 2, ETjet > 20 GeV • HT = ∑ ET jet < 80 GeV (dielectron+track analysis) Removing back-to-back leptons •  < 170 º Collaboration Meeting

  15. Missing Transverse Energy Asking three leptons Two lepton preselection not looking into signal region Missing ET Missing ET Missing transverse energy > 15 GeV Collaboration Meeting

  16. Collaboration Meeting

  17. MET ?? SIGNAL REGION 15 10 15 76 106 M() Control Regions (CR) • Definition • Investigating each CR with • high/low jet activity • 2 lepton selection • 3 lepton selection Collaboration Meeting

  18. MET ?? SIGNAL REGION 15 10 15 76 106 M() Control Regions • 2 lepton selection  + e/ low pT analysis Missing ET Collaboration Meeting

  19. MET ?? SIGNAL REGION 15 10 15 76 106 M() Control Regions • 2 lepton selection  + e/ high pT analysis Dimuon pT system Collaboration Meeting

  20. MET ?? SIGNAL REGION 15 10 15 76 106 M() Control Regions • 2 lepton selection ee+track low pT analysis Dielectron Mass Collaboration Meeting

  21. ZOOM Like-sign analysis • LS analysis acceptance • LS analysis has additional CR to test conversion removal GOOD AGREEMENT BETWEEN EXPECTED & OBSERVED Collaboration Meeting

  22. ZOOM eμ low pT analysis ee Invariant Mass • Recent analysis • First 310 pb-1 • Using SUSY dilepton dataset • Low SM backgrounds • No resonances (J/ψ,Υ ,Z) • But low statistics • Use ee and μμ CR to gain confidence in lepton selection • Careful understanding of backgrounds becomes crucial • Fake leptons • Heavy flavour production μμ Invariant Mass Collaboration Meeting

  23. ZOOM eμ low pT analysis • The low missing transverse energy region still needs better understanding • Not looked into the signal region yet eμ missing ET IN PROGRESS eμ invariant mass Collaboration Meeting

  24. LOOK in the SIGNAL REGION Collaboration Meeting

  25. Results high pT low pT Collaboration Meeting

  26. Results Collaboration Meeting

  27. Trimuon Event Collaboration Meeting

  28. Results • CDF Run II trilepton analyses • observed data compatible with SM prediction • Ready to set the limit • combine all analyses exclusively • interpret in mSugra-like scenario Collaboration Meeting

  29. Limit on the chargino mass • Degenerate slepton masses scenario • CDF Run II Limit M(1) ~ 127 GeV/c2 • D0 RunII limit in a similar scenario M(1) ~ 116 GeV/c2 • Slepton mixing scenario • Acceptance worse, no constraint yet Collaboration Meeting

  30. Conclusions and Outlook • CDF analyzed first part of data • No excess observed w.r.t. SM prediction • Limit on chargino mass beyond LEP results • But model dependent • More data & channels included by end Summer 06 • Then will go for publication • 4-8 fb-1 by the end of RunII will allow to explore chargino mass up to 250 GeV/c2 • The hunt for SUSY continue... • Stay tuned! Collaboration Meeting

  31. BACKUP SLIDES Collaboration Meeting

  32. Analyses Overview No third lepton requirement => Higher acceptance Using eμ only  very small backgrounds Sensitive to taus as 3rd lepton Collaboration Meeting

  33. Scenario light sleptons but heavy squarks M(c20)  3M(q) ~ ~ Chargino Mass Limits Fermilab-Pub-05/075-E or hep-ex/0504032 ~ ~ mSUGRA “small m0” M(  ) > M(c20) No slepton mixing • s x BR < 0.2 pb mSUGRA“large m0” M(  ) ≫M(c20) • No sensitivity A0=0 117 GeV/c2 132 GeV/c2 ~ ~ 103.5 GeV/c2 (model independent) Those limits are improved by ~10% if tau’s are included. Collaboration Meeting

  34. Systematic uncertainty • Major systematic uncertainties affecting the number of events (ee+lepton high pT) • Signal • Lepton ID 5% • Muon pT resolution 7% • Background • Fake lepton estimate method 5% • Jet Energy Scale 22% • Both signal and background • Luminosity 6% • Theoretical Cross Section 6.5-7% • PDFs 7% Collaboration Meeting

  35. The differences in the models In Standard mSugra the BR into taus is enhanced smaller acceptance Collaboration Meeting

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