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DILEPTON TRIGGERS for SUSY SEARCHES @ CDF

DILEPTON TRIGGERS for SUSY SEARCHES @ CDF. Melisa Rossi Università degli Studi di Udine & INFN. Outline. Physics Motivation What is the Standard Model? What is SUSY? SUSY Lepton-based signatures Tevatron Collider & CDF Detector CDF Trigger System SUSY DILEPTON Trigger Strategy

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DILEPTON TRIGGERS for SUSY SEARCHES @ CDF

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  1. DILEPTON TRIGGERS for SUSY SEARCHES @ CDF Melisa Rossi Università degli Studi di Udine & INFN

  2. Outline • Physics Motivation • What is the Standard Model? • What is SUSY? • SUSY Lepton-based signatures • Tevatron Collider & CDF Detector • CDF Trigger System • SUSY DILEPTON Trigger • Strategy • Structure • Trigger Monitoring • Monitoring variable • Good run list • Trigger studies • Conclusions

  3. What is the Standard Model ? An effective low energy theory that • describes matter and its interactions • combines Strong, Weak and Electromagnetic interactions • Very successful at describing data • Still unanswered questions • Where does mass comes from? • What about gravity? • What is the dark matter origin? ▬▬► Beyond the Standard Model

  4. Fermions Leptons Quarks ---------------------- Gluon ---------------------- Gauge Bosons Photon W,Z Higgs Sfermions Sleptons Squarks -------------------- Gluino -------------------- Gauginos Neutralinos Charginos What is SUSY • Possible extension of the Standard Model • Additional symmetry between fermions and bosons SM fermion field  supersymmetric boson field SM boson field  supersymmetric fermion field • Particle spectrum more than doubles

  5. What is SUSY • If SUSY was an exact symmetry • SM particle mass = corresponding superpartner mass • Clearly not realistic • No sparticles have been observed so far • Hence supersymmetry must be broken • The simplest realistic supersymmetric field theory is MSSM • Satisfies all phenomenological constraints • Depends on more than 100 parameters • Models to reduce the number of free parameters in SUSY • cMSSM, mSUGRA... • Different points in the SUSY parameter space lead to different phenomenology

  6. What is SUSY • SUSY introduces a new quantum number • R-parity: 1 for particle, -1 for sparticle • In many models R-parity is conserved • sparticles are producted in pair • Lighest superparticle is stable (LSP) • LSP behaves like a heavy neutrino • Not detectable: carrying away some energy and momentum • SUSY processes result in final states with LPS • SUSY events characterized by missing energy

  7. What is SUSY ASSUMING SUSY • LSP is an excellent candidate for cold dark matter • Coupling constants can unify at GUT scale

  8. SUSY Lepton-based Signatures • Trilepton-based • mSUGRA prediction at reach • Like-sign dileptons • Release third lepton request • Increase acceptance • LS requirement for background rejection Chargino-neutralino associated production

  9. m0 = 100 GeV, m1/2 = 180 GeV, A0 =0, tanβ=3, sgn>0 SUSY Lepton-based Signatures • Signatures characterized by • Multiple leptons • relatively low pT (<20GeV/c2) • Missing Et from multiple sources • Moderate missing Et (need full understanding of the detector) • Lepton-based Signatures very clean. This is particularly useful at hadron collider where QCD background is large.

  10. CDF D0 Tevatron Main injector & recycler Tevatron Collider • RunI (1992-1996) • ppbar √s = 1.8 TeV • luminosity peak ~1.5E31cm-2s-1 • 6x6 bunches • bunch crossing every 3.5μs • RunII (since 2001) • ppbar √s = 1.96 TeV • luminosity peak ~1E32cm-2s-1 • 36x36 bunches • bunch crossing every 396ns 6.3 km ring for a proton-antiproton collider with 980 Gev/beam

  11. Tevatron Luminosity Excellent performance in 2004 for RunII • 500 pb-1 delivered • 350 pb-1 on tape • 250 pb-1 analyzed (100pb-1 in RunI) • 4-8 fb-1 by 2009 Plan for~1.5E32cm–2s–1 luminosity peak by the end of 2005

  12. The CDF Detector • Retained from RunI • central and endwall calorimeter • central muon system • solenoid New in RunII • tracking system • central outer tracker (COT) • silicon vertex detector (SVX+ISL) • Endplug calorimeter • Muon system upgrade • Front-end electronics • DAQ/Trigger system

  13. Path 2 Path 1 L1 trigger L1 trigger L2 trigger L2 trigger L3 trigger L3 trigger Dataset CDF Trigger System • Trigger • combines information from all subdetectors (tracking, calorimeter, muon chambers...) • takes online decision to keep or reject events • CDF Technical constrains • Rate limits • CDF developed • 3 level trigger system • organized in • Path = unique combination of L1,L2,L3 • Dataset = combination of paths

  14. CDF Detector 7.6 million events/sec L1 pipeline 5.5μs 50kHz L2 decision 20μs 300Hz L3 decision 600ms 75Hz OFFLINE CDF Trigger System • Accept rates are 10x higher than RunI • L1+L2 rejection factor is 20000:1 • The trigger budget is balanced between all the physics groups (bandwidth distribution) @1E32cm–2s–1 Rate = Inst. Lumi. x cross section

  15. CDF Trigger System • Level 1 information • Calorimeter • trigger towers Δη x Δφ = 0.2 x 15 • Global trigger: missing Et, SumEt • Tracking (eXtremelyFastTracker) • Efficiency> 96% for pT>1.5GeV/c • Muon = 2D track matched to stub • Stub = cluster of hits in muon chamber • Electron = 2D track matched to trigger tower • Level 2 information • Calorimeter clustering algorithm • Identify seed towers • Identify shoulder towers • Silicon vertex tracker • To identify displaced tracks • Impact parameter resolution 35μm • Muon boards • New L2 code in 2004 • Level 3 information • Offline-like reconstruction

  16. SUSY DILEPTON Trigger • SUSY Lepton-based signals • low pt multilepton final states • Ideal choice would be an inclusive lepton trigger • CDF opted for a multipath DILEPTON trigger • To fit with bandwidth available resources • To achieve the maximum acceptance/efficiency  The SUSY DILEPTON Dataset

  17. SUSY DILEPTON Trigger Lepton types involved in the trigger • CEM4 central electron with 4GeV/c pt • CEM8 central electron with 8GeV/c pt • PEM8 forward electron with 8GeV/c et • CMU4 muon with 4GeV/c pt (η<0.6) • CMUP4 muon with 4GeV/c pt (η<0.6) • CMX4 muon with 4GeV/c pt (0.6<η<1)

  18. SUSY DILEPTON Trigger • Lepton types combined in 20 trigger paths • CEM4_CMU4 • CEM4_CMUP4 • CEM4_CMX4 • CEM4_PEM8 • CMU4_PEM8 • CMUP4_PEM8 • CEM4_CEM4 • .......

  19. SUSY DILEPTON Trigger Trigger issues are • Monitoring generally a study for each path, • Calibration complex with a multipath structure!! • We followed a new strategy to simplify calibration • define a lepton object for each lepton type • definitions do not depend on the specific path • compute efficiency for each lepton object • combine lepton objects into trigger paths

  20. SUSY DILEPTON Trigger lepton object = standard single lepton definition @ trigger level 20 trigger paths 6 lepton objects electrons muons

  21. SUSY DILEPTON Trigger • SUSY Trigger organized in 3 categories • A : baseline paths • Ask for 2 leptons of 4GeV/c pt at L1, L2, L3 • B : complementary paths • Ask for 1 lepton + an additional track of 8 GeV/c pt at L1 and L2 • To recover stub/cluster inefficiency • C : complementary paths • Ask for 1 lepton of 12 GeV/c pt at L1 and L2 • To increase the acceptance • All paths contribute to the acceptance

  22. SUSY DILEPTON Trigger • Trigger cross section: • L2 700 nb • L3 80 nb @7.5E32cm–2s–1

  23. Trigger Monitoring • Monitoring the performance of a trigger is important • to check the quality of the collected events • to verify the stability in time of the trigger response • to keep track of trigger changes • Need of a suitable Monitoring Variable

  24. Trigger Monitoring • Monitoring Approach • Consider events collected by each of the trigger path • Verify which leptons are reconstructed @ offline level For each trigger path Trigger level Offline level 2 lepton objects found 2 leptons reconstructed

  25. Trigger Monitoring • Each DILEPTON Trigger path requires • lepton1 & lepton2 @ trigger level • For each trigger path: • D1 = number of collected events • N1 = number of collected events with lepton 1 reconstructed offline and same quantities for lepton 2

  26. Trigger Monitoring • Monitoring Variable: R • It separate information about lepton1 and lepton 2 • It is a sort of purity • 0 < R < 1 • higher R  higher quality of the collected events • In ideal conditions R = 1 • It is expected to be stable in time • We have several R values for each lepton type • expect no significant differences between different trigger paths R1 = N1/D1 R2 = N2/D2

  27. Trigger Monitoring R distribution vs. Time (run) for CEM4 PATH:CEM4_PEM8 PATH:CEM4_CMUP4 ► R is locally stable in time ► Steps in distribution correlated to trigger changes ► changes increase R value higher quality ► similar absolute R values for a given lepton type

  28. SUSY TRIGGER Monitoring • R behaves as expected • We can use it as discriminator for a good/bad run • For each lepton object we define a suspect run • Test for R indipendence of trigger path • Test for R stability in time

  29. 1 R Rlepton run SUSY TRIGGER Monitoring • Supect run definition for each lepton object • R indipendence of trigger path • R = value for each trigger path • Rlepton= average value for each run • The run is suspect if |R-Rlepton| > 10σ • R stability • <Rlepton> = Rlepton local average over 20 runs • The run is suspect if |Rlepton-<Rlepton>| > 5σ 1 2 2 run1 run2 run3

  30. SUSY TRIGGER Monitoring total suspect luminosity 37pb-1 out of 380 pb-1 considered Suspect run luminosity for lepton object Rlepton stability CEM4

  31. Growth terms Constant σ Constant rate SUSY DILEPTON Trigger Studies • CDF is facing high luminosity scenarios • trigger cross sections depend on luminosity • possible growth factor @ high luminosity • For any process rate R = L σ • For a physics process σ independent of L • For trigger cross sections, observe: σ = A / L + B + C L + D L2 Growth factor in trigger cross section

  32. SUSY DILEPTON Trigger Studies • For SUSY DILEPTON Trigger • Possible large growth factor @ L2 • In particular for complementary paths • We performed a L2 Study • Total and exclusive cross section behaviour with luminosity • High-pt inclusive muon: L2_CMUP6_PT8 • High-pt inclusive electron: L2_CEM12_PT8 • Medium-pt electron+track: L2_CEM8_PT8_CES3_&_TRK8 exclusive cross section = effective cross section @ L2 w.r.t. the whole CDF trigger

  33. L2_CMUP6_PT8 L2_CEM8_PT8_CES3_&_TRK8 σTOT σTOT σEX σEX • Inclusive muon: • No major growth factor • Used by variety of physics group (not only exotic) • Electron+track: • σTOT rises with L • Adds very little to global L2 bandwidth L2 X-SECTIONS (nb) vs. L (cm-2s-1)

  34. L2_CEM12_PT8 σTOT σEX L2 X-SECTIONS (nb) vs. L (cm-2s-1) • Inclusive electron: • No growth factor in σtot • σEX≤ 100nb

  35. Summary -1- • Physics motivation for SUSY • multiple leptons final states • DILEPTON Trigger for SUSY @ CDF • Complex Multipath trigger structure • New strategy • Standard lepton object definition • To simplify calibration and monitoring

  36. Summary -2- • SUSY DILEPTON Trigger Monitoring • Variable choice: R • gives information about event quality • behaves as expected • locally stable in time • steps correlated to trigger changes • Good run list per lepton object done • 37pb of suspect luminosity (10% of the total) • Ready for Trigger Calibration

  37. Summary -3- • SUSY DILEPTON trigger up to shutdown ’04 • Complementary paths are healthy • No appreciable growth factors • Small effective cross sections • CDF should be ready for 1.5E32cm-2s-1 • the whole CDF trigger will be revised • need to re-think also the SUSY trigger for 2005 fall

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