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Melisa Rossi Udine University Ph.D. Thesis Defense Udine – June 14, 2006

Search for Chargino and Neutralino production in the trilepton channel with the CDF Run II detector. Melisa Rossi Udine University Ph.D. Thesis Defense Udine – June 14, 2006. Contents. Supersymmetry The trilepton signature The CDF detector The CDF trigger system The SUSY DILEPTON trigger

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Melisa Rossi Udine University Ph.D. Thesis Defense Udine – June 14, 2006

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  1. Search for Chargino and Neutralino production in the trilepton channel with the CDF Run II detector Melisa Rossi Udine University Ph.D. Thesis Defense Udine – June 14, 2006 Ph.D. Thesis Defense

  2. Contents • Supersymmetry • The trilepton signature • The CDF detector • The CDF trigger system • The SUSY DILEPTON trigger • Monitoring & Efficiencies • Trilepton analysis @ CDF • The approach • The eμ low pT channel • CDF Run II Limit on chargino mass • Conclusions and outlook The Physics Subject The Tools The Search In conclusion Ph.D. Thesis Defense

  3. The Physics Subject Ph.D. Thesis Defense

  4. Supersymmetry • 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 • a framework for unification • a dark matter candidate • No evidence of SUSY yet • must be a broken symmetry Ph.D. Thesis Defense

  5. 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 Ph.D. Thesis Defense

  6. Tevatron Cross sections (pb) m (GeV) SUSY cross sections are small! σ(SUSY) ~ pb while σ(pp) ~ 50 x 109 pb _ 100 events per fb-1 Concentrating on chargino and neutralino Ph.D. Thesis Defense

  7. +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 Ph.D. Thesis Defense

  8. Multilepton Final States • Multi-lepton signatures • appealing for other SUSY searches • RPV SUSY processes • very clean • particularly powerful @ hadron colliders where QCD background dominates • but leptons from chain decays • relatively low pT(< 20 GeV/c) 1 pb Ph.D. Thesis Defense

  9. The Tools Ph.D. Thesis Defense

  10. CDF DO The Tevatron Accelerator Ph.D. Thesis Defense

  11. The CDF Run II Detector • Multipurpose Detector • precision tracking • good calorimeter & μcoverage • Electrons |η| < 3.6 • Muons |η| <1.5 Ph.D. Thesis Defense

  12. CDF Detector 7.6 million events/sec L1 pipeline 5.5μs 25kHz L2 decision 20μs 300Hz L3 decision 600ms 75Hz OFFLINE CDF Trigger System • 3-level architecture • to minimize deadtime • path = unique combination of L1,L2,L3 • accept rates are 10x higher than RunI • L1+L2 rejection factor is 20000:1 @1E32cm–2s–1 Ph.D. Thesis Defense

  13. ELECTRONS MUONS Leptons @ Trigger Level • Muon/Electron @ Trigger Level • Muon = track compatible with mip matched to stub • stub = set of hits in muon chamber • Electron = track matched toem deposition in calorimeter Ph.D. Thesis Defense

  14. DILEPTON trigger Trigger Cross Section inclusive low pT lepton trigger not feasible, then • DILEPTON trigger (electrons and muons) • highly redundant (~20 trigger paths) • maximize acceptance (geometry and efficiency) • easier to understand trigger • comparisons between paths • calibration and monitoring samples in the same data set • extraction of unbiased lepton samples • detector conditions naturally folded in @1E32cm–2s–1 Ph.D. Thesis Defense

  15. DILEPTON trigger layout • baseline - workhorse • to recover stub/cluster inefficiency • to increase the acceptance 20 trigger paths • CEM4_CMU4 • CEM4_CMUP4 • CEM4_CMX4 • ...... • CEM4_CMX4_L2_CEM8_TRK8 • CEM4_CMU4_L2_CEM8_TRK8 • ....... • CEM4_CEM4_L2_CEM12 • CEM_PEM8_L2_CEM12 A B C Ph.D. Thesis Defense

  16. 6 lepton types 20 trigger paths DILEPTON trigger strategy • define lepton types • do not depend on the specific path • trigger studies for each lepton type • combine single lepton type results into trigger paths Monitoring & Efficiency Calculation for each lepton type Ph.D. Thesis Defense

  17. steps in distributions indicatives of trigger changes 4 GeV Central Electron RCEM4 Run Number change in trigger for ETcalculation Monitoring • defining a suitable variable for each lepton type • sort of purity • expected to be stable in time • also different estimations for each lepton type • provide cross checks between paths Ph.D. Thesis Defense

  18. e- e+ Calorimeter & Tracking Calorimeter only γ CENTRAL CENTRAL FORWARD FORWARD Efficiency Calculation • Calculated efficiency for L1 L2 electron lepton types • Used conversion electrons as probe • must satisfy ID cuts • must be unbiased for the trigger being calibrated • must come from a conversion • each electron associated with a track (|Δcotθ|<0.15 , Sxy<0.1) Ph.D. Thesis Defense

  19. The Search Ph.D. Thesis Defense

  20. 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 at DATA in the SIGNAL REGION compare number of predicted and observed events Ph.D. Thesis Defense

  21. Ph.D. Thesis Defense

  22. 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 Ph.D. Thesis Defense

  23. I. The eμ low pT analysis • This thesis focuses on • Events with at least • 1 identified electron and 1 identified muon • CEM4_CMUP4 trigger path • part of the SUSY DILEPTON trigger • central electron |η|<1.1 and central muon |η|<0.6 • 224 pb-1 collected between 2002 and 2004 • The eμ channel has low SM backgrounds • Heavy flavour and diboson production • Fakes contribution becomes more important than in other analyses • But low statistics Ph.D. Thesis Defense

  24. II. Backgrounds • 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 • Drell-Yan production + additional lepton • Leptons cover a wide range in pT • Small missing transverse energy • Low jet activity SM processes yielding to eμ final states Irreducible Other processes yielding to eμ final states • Fake leptons • Conversion electrons Ph.D. Thesis Defense

  25. III. Basic Analysis Selection • Two lepton preselection • leading lepton pT>10 GeV/c • next-to leading pT>5 GeV/c • Missing Transverse Energy • missing ET > 15 GeV • Third Lepton Requirement • third lepton pT > 5 GeV/c Ph.D. Thesis Defense

  26. Ph.D. Thesis Defense

  27. MET ?? SIGNAL REGION if 3 leptons 15 10 < 2 > 1 Number of Jets 15 76 106 M() Control Regions (CR) • CR in terms of • missing ET (high, low) • Njet(high, low) • number of leptons • 2 lepton selection • 3 lepton selection • separating events between • like sign (LS) and opposite sign (OS) charge • Additional high statistics CR to test lepton selection • ee and μμ events • full invariant mass spectrum • Z window mass Ph.D. Thesis Defense

  28. 15 76 106 M() Control Regions (ee) Ph.D. Thesis Defense

  29. 15 76 106 M() Control Regions (μμ) Ph.D. Thesis Defense

  30. Control Regions (eμ) OS 2 lepton selection MET ?? 15 10 LS < 2 > 1 Number of Jets Ph.D. Thesis Defense

  31. Control Regions (eμ) OS 2 lepton selection MET ?? 15 10 LS < 2 > 1 Number of Jets Ph.D. Thesis Defense

  32. Control Regions (eμ) OS 2 lepton selection MET ?? 15 10 OS < 2 > 1 Number of Jets Ph.D. Thesis Defense

  33. eμ low pT analysis status • The low missing transverse energy region still needs better understanding • Need more bbbar MC • Possible fakes underestimation • Not looked into the signal region yet OS LS Ph.D. Thesis Defense

  34. Other Trilepton Analyses LOOKED in the SIGNAL REGION Good agreement between observed and predicted events Ph.D. Thesis Defense

  35. Other Trilepton Analyses LOOKED in the SIGNAL REGION SET CHARGINO MASS LIMIT • Combine all analyses exclusively • 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 Ph.D. Thesis Defense

  36. Conclusions and Outlook In conclusion • The trilepton signature is SUSY Golden channel at the Tevatron • This thesis focuses on eμ final states • Low SM backgrounds BUT low statistics • Low missing ET region still needs some work • CDF Run II Limit on chargino mass beyond LEP results • But model dependent • Want to finish the analysis by end Summer 06 • …. and be in the publication! • 4-8 fb-1 by the end of RunII will allow to explore chargino mass up to 250 GeV/c2 Ph.D. Thesis Defense

  37. BACKUP SLIDES Ph.D. Thesis Defense

  38. Analyses Overview No third lepton requirement => Higher acceptance Using eμ only  very small backgrounds Sensitive to taus as 3rd lepton Ph.D. Thesis Defense

  39. 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. Ph.D. Thesis Defense

  40. The differences in the models In Standard mSugra the BR into taus is enhanced smaller acceptance Ph.D. Thesis Defense

  41. 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% Ph.D. Thesis Defense

  42. TRIGGER PATH LIST • cem4_cmu4 • cem4_cmu4_l2_cem8_pt8_ces2_&_trk8 • cem4_cmu4_l2_trk8_l1_cmup6_pt4 • cem4_cmup4 • cem4_cmx4 • cem4_cmx4_l2_cem8_pt8_ces2_&_trk8 • cem4_pem8 • cem4_pem8_l2_cem12_pt8 • cem8_pem8 • cmu4_pem8 _ • cmu4_pem8_l2_trk8_l1_cmup6_pt4 • cmup4_pem8 • cmx4_pem8 • dielectron_central_4 • dielectron_central_4_l2_cem12_pt8 • dielectron_central_4_l2_cem8_pt8_ces2_&_trk8 • dimuon_cmu4_cmx4 • dimuon_cmu4_cmx4_l2_trk8_l1_cmup6_pt4 • dimuon_cmucmu4 • dimuon_cmucmu4_l2_trk8_l1_cmup6_pt4 • dimuon_cmup4_cmx4 • dimuon_cmupcmup4 Ph.D. Thesis Defense

  43. 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 Ph.D. Thesis Defense

  44. Control Regions – Summary Ph.D. Thesis Defense

  45. L1 Electron Primitives Trigger Requirements • L1 4 GeV Central Electron • Calorimeter Trigger Tower • ET≥ 4 GeV • Ehad / Eem≤ 12.5% • Track • PT≥ 4 GeV/c • L1 8 GeV Forward Electron • Calorimeter Trigger Tower • ET≥ 8 GeV • Ehad / Eem≤ 6.25% em em Ph.D. Thesis Defense

  46. e- e+ γ Probe Electrons • Must satisfy ID cuts • Must be unbiased for the trigger being calibrated i.e. events collected by triggers unrelated to the one tested • Must come from a conversion • each electron associated with a track requiring • |Δcotθ|<0.15 , Sxy<0.1 • Consider 2 sub-samples • Peak |Δcotθ|<0.03 (Electrons+Fakes) • Sideband |Δcotθ|>0.05 (assuming Fakes only) Ph.D. Thesis Defense

  47. Calorimeter & Tracking Calorimeter only CENTRAL CENTRAL FORWARD FORWARD L1 Trigger Efficiency • Central electron efficiency • plateau value ~ 90% due to tight track requirement Forward electron efficiency • slow turn-on due to online-offline energy difference FORWARD Ph.D. Thesis Defense

  48. Back-up Plug Conversion Selection Ph.D. Thesis Defense

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