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

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

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

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

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

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

July 19, 2005SUSY05 – T. Adams7 DØ Detector

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

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 ns for different layers –causes inefficiency for slower moving particles –efficiency drops as mass increases –sufficient for our mass range ( GeV)

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

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

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

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

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

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

July 19, 2005SUSY05 – T. Adams16 Analysis Results Background estimated using data Stau Mass (GeV)Background EstimateData Events ± 0.7 ± ± 0.06 ± ± 0.05 ± ± 0.04 ± ± 0.03 ± ± 0.05 ± 0.020

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

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

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

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

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