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

2. July 19, 2005SUSY05 – T. Adams2 Tevatron pp collisions at 1960 GeV detectors: –DØ and CDF recorded luminosity ~8 times Run I _

3. July 19, 2005SUSY05 – T. Adams3 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

4. July 19, 2005SUSY05 – T. Adams4 GMSB Model stable stau: NLSP (LSP is gravitino/goldstino) large value of C grav Snowmass 2001 Model Line D mm scale of SUSY breaking19 to 100 TeV MmMm messenger mass scale 2m2m N5number of messenger fields3 tan  ratio of Higgs VEVs15 sign  sign of higgsino mass term+1 C grav factor for effective mass of gravitino>>1

5. July 19, 2005SUSY05 – T. Adams5 Chargino Model stable chargino –higgsino-like or –gaugino-like higgsino-likegaugino-like  (GeV) 60-30010,000 M 1 (GeV)100,0003M 2 M 2 (GeV)100,00060-300 M 3 (GeV)500 tan  15 squark mass (GeV) 800 small (<150 MeV) mass difference between lightest chargino and lightest neutralino

6. July 19, 2005SUSY05 – T. Adams6 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

7. July 19, 2005SUSY05 – T. Adams7 DØ Detector

8. July 19, 2005SUSY05 – T. Adams8 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 1 st and 2 nd layers CMSP’s will be out-of-time

9. July 19, 2005SUSY05 – T. Adams9 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)

10. July 19, 2005SUSY05 – T. Adams10 Preliminary Dimuon Selection muon p T > 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 Luminosity = 390 pb -1

11. July 19, 2005SUSY05 – T. Adams11 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

12. July 19, 2005SUSY05 – T. Adams12 Speed Significance Data muons CMSP

13. July 19, 2005SUSY05 – T. Adams13 Backgrounds Z/Drell-Yan is major background –no natural source of slow-moving high-p T particles Use data to estimate background –use Z-peak events for timing distribution –use negative time events for invariant mass distribution

14. July 19, 2005SUSY05 – T. Adams14 Transverse Momentum Signal has larger p T

15. July 19, 2005SUSY05 – T. Adams15 Dimuon p T vs Significance Product Significance product: Sig(  1 ) x Sig(  2 ) 60 GeV stau’s Real muon data

16. July 19, 2005SUSY05 – T. Adams16 Analysis Results Background estimated using data Stau Mass (GeV)Background EstimateData Events 6013.6 ± 0.7 ± 0.513 1000.66 ± 0.06 ± 0.020 1500.69 ± 0.05 ± 0.020 2000.60 ± 0.04 ± 0.020 2500.47 ± 0.03 ± 0.020 3000.61 ± 0.05 ± 0.020

17. July 19, 2005SUSY05 – T. Adams17 stau Cross-section Limit Best limit from the Tevatron

18. July 19, 2005SUSY05 – T. Adams18 Charginos Charginos look like stau’s Use same analysis

19. July 19, 2005SUSY05 – T. Adams19 Chargino Limits Higgsino-likeGaugino-like M > 140 GeV M > 174 GeV DØ RunII Preliminary

20. July 19, 2005SUSY05 – T. Adams20 Effect of Lifetime “Short” lifetime  decay within detector loss of acceptance

21. July 19, 2005SUSY05 – T. Adams21 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