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Search for Long-Lived Particles at D Ø

This presentation discusses the search for long-lived particles that do not decay within the detector and have a unique signature. It explores the models of GMSB, specifically stau and chargino, and discusses the optimization for pair production. The DØ detector and the muon system are described, along with the trigger and preliminary dimuon selection. Background estimation and analysis results are presented, along with the cross-section limit for stau and chargino.

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Search for Long-Lived Particles at D Ø

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  1. Search for Long-Lived Particles at DØ Todd Adams Florida State University July 19, 2005 SUSY05 IPPP Durham

  2. Tevatron _ • pp collisions at 1960 GeV • detectors: • DØ and CDF recorded luminosity ~8 times Run I SUSY05 – T. Adams

  3. Introduction • Search for long-lived particles • “stable” = doesn’t decay within the collider detector • can still decay • massive (>50 GeV) • charged particles = unique signature • SUSY models • GMSB: stau • chargino • optimize for pair production SUSY05 – T. Adams

  4. GMSB Model • stable stau: NLSP (LSP is gravitino/goldstino) • large value of Cgrav • Snowmass 2001 Model Line D SUSY05 – T. Adams

  5. Chargino Model • small (<150 MeV) mass difference between lightest chargino and lightest neutralino • stable chargino • higgsino-like or • gaugino-like SUSY05 – T. Adams

  6. Charged Massive Stable Particles(CMSPs) • Massive: >50 GeV • Slow-moving:  < 1 • Charged: large energy deposition • Bethe-Block formula • Long-lived: decays outside of muon detector • Will look like slow moving muon SUSY05 – T. Adams

  7. DØ Detector SUSY05 – T. Adams

  8. Muon System • Detects minimum-ionizing particles • Timing: speed of light particle will register at t=0 in all three layers • resolution is 2-3 ns • Three layers • Toroid between 1st and 2nd layers • CMSP’s will be out-of-time SUSY05 – T. Adams

  9. Trigger • Trigger requires two tracks in muon system • Timing issues: • trigger gate is asymmetric • allows later particles • trigger gate ranges from 20-85 ns for different layers • causes inefficiency for slower moving particles • efficiency drops as mass increases • sufficient for our mass range (60-300 GeV) SUSY05 – T. Adams

  10. Preliminary Dimuon Selection Luminosity = 390 pb-1 • muon pT > 15 GeV • matched to track in central tracker • scintillator hits in 2 of 3 layers of muon system • at least one isolated muon •  > 1.0 radians • cosmic ray muon rejection SUSY05 – T. Adams

  11. Muon Speed • Calculate speed of muon at each layer • v = d/t (v in units of c) • v from timing error • Calculate average velocity for each muon • Calculate speed 2 • Require 2 < 4 SUSY05 – T. Adams

  12. Speed Significance Data muons CMSP SUSY05 – T. Adams

  13. Backgrounds • Z/Drell-Yan is major background • no natural source of slow-moving high-pT particles • Use data to estimate background • use Z-peak events for timing distribution • use negative time events for invariant mass distribution SUSY05 – T. Adams

  14. Transverse Momentum Signal has larger pT SUSY05 – T. Adams

  15. Dimuon pT vs Significance Product • Significance product: Sig(1) x Sig(2) 60 GeV stau’s Real muon data SUSY05 – T. Adams

  16. Analysis Results • Background estimated using data SUSY05 – T. Adams

  17. stau Cross-section Limit Best limit from the Tevatron SUSY05 – T. Adams

  18. Charginos Charginos look like stau’s Use same analysis SUSY05 – T. Adams

  19. Chargino Limits Higgsino-like Gaugino-like M > 140 GeV M > 174 GeV DØ RunII Preliminary SUSY05 – T. Adams

  20. Effect of Lifetime • “Short” lifetime  decay within detector • loss of acceptance SUSY05 – T. Adams

  21. Conclusions • DØ has performed a search for charged, massive stable particles • look for slow moving particles • Set limits on stau and chargino production • best limits on chargino mass SUSY05 – T. Adams

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