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Search for Anomalous Production of Multi-lepton Events at CDF

Search for Anomalous Production of Multi-lepton Events at CDF. Alon Attal UCLA Sept. 5, 2006. Outline. Standard Model SUSY Theory & Motivation CDF Detector Signal & Background Analysis Results. Standard Model. The Standard Model (SM): SU(3) x SU(2) x U(1) Y

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Search for Anomalous Production of Multi-lepton Events at CDF

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  1. Search for Anomalous Production of Multi-lepton Events at CDF Alon Attal UCLA Sept. 5, 2006

  2. Outline • Standard Model • SUSY Theory & Motivation • CDF Detector • Signal & Background • Analysis • Results Alon Attal

  3. Standard Model • The Standard Model (SM): SU(3) x SU(2) x U(1)Y • The SM agrees extraordinarily well with detector measurements • SM requires a Higgs boson to explain massive particles • Is there physics beyond the SM? Alon Attal

  4. New Physics Clues • SM does not contain gravity • New physics at Planck Scale (~1018 GeV) • Higgs has not been discovered yet • Could be an indication of non-SM Higgs • Hierarchy problem • Unnatural for Higgs mass corrections to depend on Planck Scale • Dark Matter • None of the particles within SM can account for it • Particle – antiparticle asymmetry • Can’t be accounted for with SM CP violation • Particle masses, quantized electric charge, 3 families • SM doesn’t answer why it is the way it is Alon Attal

  5. SuperSymmetry (SUSY) is a proposed symmetry between fermions and bosons: Fermions Bosons SM particles SUSY particles SM particles/Higgs SUSY particles What is SuperSymmetry? SUSY contains particles exactly the same as Standard Model particles but with different spin: SUSY must be broken  particles gain mass Alon Attal

  6. f H H H H - f  particles should have masses on the order of Mtop SUSY Motivation SUSY cancels quadratic divergences in the Higgs sector: ≈ 0 Works best when particle, SM masses are similar Alon Attal

  7. SUSY Grand Unification SM ai-1(m) m (GeV) Addition of particles leads to unification at GUT Scale Alon Attal

  8. ~ c0 1 Minimal Supergravity (mSUGRA) • SUSY introduces > 100 free parameters • The mSUGRA framework constrains the theory down to 5: M0,M1/2,tanb,A0,sign(m). • In my analysis M( ) is the most important and depends on M1/2 Alon Attal

  9. +1 for SM particles Rp = (-1)[3(B-L) + 2S] -1 for particles B = baryon #, L = lepton #, S = spin R-Parity (Rp) If Rp is conserved, the lightest supersymmetric particle (LSP) is stable. LSP = Dark Matter candidate Alon Attal

  10. Only consider Li Lj Ek term, protecting proton lifetime • |λ| < 0.1, assume only LSP decays via RpV coupling R-Parity Violation (RpV) “RpV SUSY is no WIMP” 3 additional couplings: Violates baryon # Violate lepton # Alon Attal

  11. 2 particles 4-Lepton SignatureStep 1: Dominant Sparticle Production p p Alon Attal

  12. 2 particles Step 2: Chargino/Neutralino Decay Leptons may be produced in cascade decays. p p cascade decay 2 LSPs Alon Attal

  13. l121diagrams: 2 particles Step 3: RpV Decays Most sensitive to l121 and l122. p p cascade decay 2 LSPs RpV decay ≥ 4 Charged Leptons Alon Attal

  14. Restrictions on l • There are theoretical and experimental limits on l: • Upper limit set by muon lifetime • Lower limit set by impact parameter cut on identified leptons (d0 ≤ 0.02 cm) • Analysis is not sensitive to the specific value of l since Alon Attal

  15. Tevatron & Luminosity 346 pb-1 used Currently the highest energy accelerator in the world Alon Attal

  16. Lepton ID important to analysis Studied in data and MC Efficient (~90%) Probability that jets are misidentified as leptons is small (< 0.02%) CDF Detector & Lepton ID • Electrons • Track + Calorimeter Cluster • 95% of energy in EM calorimeter • |η| < 2.0 • Muons • Track plus “stub” in muon detector • Minimum ionizing • |η| < 1.1 η = 0 η = 1.0 η = 2.0 Calorimeter Drift Chamber Muon Detectors ~ Alon Attal

  17. ~ c0 1 Signal Distributions Analysis Reference Point: M0 (GeV) M1/2 (GeV) tanβ sign A0 M (GeV) M (GeV) M (GeV) ~ s (pb) ~ c± c0 1 2 250 260 5 + 0 99.4 182.2 181.4 0.13 electron coverage muon coverage Alon Attal

  18. Needle in a Haystack • SUSY σmuch smaller than backgrounds • Key: understand and reduce backgrounds Alon Attal

  19. Data Collection All Events High-pT lepton triggers: Electron or muon with pT > 18 GeV/c Triggered Events Dilepton Filter: “Tight” lepton w/ pT > 18 GeV/c and “loose” lepton w/ pT > 5 GeV/c Filtered Events Alon Attal

  20. Backgrounds (Before Final Cuts) Luminosity = 346 pb-1 • Individual processes • t-tbar / heavy flavor • Diboson • Composite backgrounds • W / Z/g* + Misidentified Jets • Determined from data • W / Z/g* + Photon Conversions (g + material → e+e-) • Determined from MC Alon Attal

  21. Analysis Strategy Goal: Find new physics in multi-lepton channel! • Counting experiment with 346 pb-1 • No Jet or missing energy cuts to reduce model dependency • Also sensitive to H±± and non-minimal SUSY models • Two signal regions “boxes” to optimize result: • 4 or more leptons • Exactly 3 leptons (to increase acceptance) • Choose selection criteria to optimize S/B • Validate with control regions Alon Attal

  22. Selection Criteria & Targeted Backgrounds Selection Requirement Drell-Yan Z/g + g Jets Heavy Flavor Di-Boson U, J/y      ET (pT) > 20, 8, 5 GeV/c2 (GeV/c) for 1st, 2nd, additional leptons, respectively Trilepton Signal Regions: At least one of the two leading leptons must be an e± (m±) for l121 (l122)   Z Veto Cut: ≠ (76 < Ml+l- < 106 GeV/c2) Df Cut: ≠ ( 160 < Df < 200°)      Isolated Leptons   Low Mass Cut: Mll < 15 GeV/c2 Electron track + opp. sign partner track: S < 0.1 cm, Dcotq < 0.02  Alon Attal

  23. Systematic Uncertainties • Understanding uncertainties important for reporting the accuracy of the result • Largest systematic uncertainties: • Mis-ID Jets for background expectation • Lepton ID for signal expectation Alon Attal

  24. Control Region (Example) • Control regions are crucial to understanding our procedure • Validate lepton ID efficiencies • Validate selection cuts Trilepton events that fail 1 or more cuts Alon Attal

  25. Each point corresponds to a single control region w/ error bars = ±1σ Control Region Overview • 26 total control regions (summary on left) • By lepton type • Inside & outside Z window • Number of leptons • Pass/Fail Df cut • Analysis procedure is validated through agreement between data and MC prediction y = x Alon Attal

  26. Opening the Box ? Alon Attal

  27. Signal Regions • Signal events: 4 eee, 1eem, 1 mme • Probability of observing ≥ 5 events with 3.1 expected = 17% • Signal regions consistent with background and no signal Alon Attal

  28. Setting Limits • Use Bayesian method to find σobs, combining 3 and ≥4 lepton signal regions • Set limits for multiple SUSY scenarios Alon Attal

  29. Results Alon Attal

  30. Jet 16 GeV e- 50 GeV e- 13 GeV e+ 30 GeV Trilepton Event e- 50 GeV,e+ 30 GeV,e- 13 GeV Jet 16 GeV e- 50 GeV Leading Mee = 70 GeV/c2 Jet 16 GeV e+ 30 GeV ET = 1.5 GeV e- 13 GeV Alon Attal

  31. Trilepton Invariant Mass Trilepton Signal Events Alon Attal

  32. DØ RpV SUSY Search • DØ searched for same process but in 3l + ET channel • Disadvantages: • Sensitive to less areas of new physics • Overlap with Rp conserving search • Advantages: • Missing energy cut reduces Z/g* background • Better limits Alon Attal

  33. Rp Conserving SUSY Searches • CDF and DØ both have conducted searches for associated production of chargino-neutralino events • Results combine 3l + ET and like l±l± ET searches Alon Attal

  34. ~ c± 1 Comparing Limits Experiment Rp Signature Luminosity (pb-1) M( ) Limit (GeV/c2) CDF Conserved 3l + ET 310-750 127 DØ Conserved 3l + ET 300-1,100 140 LEP Violated 450 103 CDF Violated ≥ 3l 350 186-203 DØ Violated 3l + ET 360 229-234 • RpV mass limits > RpC mass limits • Small branching ratio into leptons • El from LSP decay > El from cascade decays • DØ RpC mass limits > CDF mass limits • Expected limits are similar • DØ assumes no slepton mixing Alon Attal

  35. Conclusions • We completed a search for new physics in the multilepton channel • No significant evidence of physics beyond the SM was detected • We set mass limits on the lightest neutralino and chargino using an RpV SUSY framework • 1st draft approved by internal review committee and sent to collaboration for review on 8/2/06 Alon Attal

  36. Backup Alon Attal

  37. particle Masses Alon Attal

  38. mSUGRA Parameter Dependence Alon Attal

  39. Electron ID Cuts Alon Attal

  40. Muon ID Cuts Alon Attal

  41. Exactly 2 opp. Sign electrons Z Mass Window Additional Control Regions Trilepton events that fail 1 or more cuts Alon Attal

  42. 26 total control regions (summary on left) By lepton type Inside & outside Z window Number of leptons Pass/Fail Df cut Analysis procedure is validated through agreement between data and MC prediction Control Region Overview StMu = Stubbed Muon, X = electron or muon Alon Attal

  43. Limits ~ ~ c0 c± 1 1 Alon Attal

  44. ~ ~ c0 c± 1 1 DØ Limits Alon Attal

  45. ET = 2.2 GeV Trilepton Event 2 Jet #1 e- - Jet #1 Jet #2 e+ Jet #3 - e+ e- Alon Attal

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