Carsten Rott , Purdue University For the CDF Collaboration and LEP Experiments - PowerPoint PPT Presentation

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Carsten Rott , Purdue University For the CDF Collaboration and LEP Experiments

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  1. Search for top and bottom squarks Carsten Rott, Purdue University For the CDF Collaboration and LEP Experiments International Europhysics Conference on High Energy Physics, Aachen, 2003

  2. Light Stop Large mass splitting Light Sbottom down type quarks up type quarks Large tanb SUSY Motivation • SUSY is a possible extension of the Standard Model to achieve unification • SUSY parameters: • Ratio of vac. exp. values of two Higgs doublets: • gaugino mass parameter: • common mass for scalar fermions at GUT scale: • Higgsino mixing parameter: • Trilinear coupling in the Higgs sector: Third generation sparticles could be light, due to large mixing • Mass matrix mixing term DM = mass diff. of squark under investigation to LSP

  3. Stop and Sbottom Searches • Stop and Sbottom Searches at LEP II • Sbottom • Stop (three-body decay) • Stop (two-body decay) • Stop summary (two & three-body decays) • Stop (four-body decay) • Stop nearly mass degenerated • Stop and Sbottom searches at the Tevatron • Run I • Stop Search with OS dileptons • RP-violating stop • Run II • Search for long lived stop • Sbottom from gluino decays

  4. * max coupling * min coupling max coupling min coupling Stop and Sbottom Production at LEP II LEP EWK produced SUSY Year Ecm <L/Exp> [GeV] [pb-1] 1996 161-172 ~ 20 1997 183 ~ 55 1998 189 ~170 1999 192-202 ~230 2000 204-209 ~227 Production x-section depends on mass and mixing angle

  5. L3 Note 2804 CERN-EP/2003-007 Select two high multiplicity acoplanar jets Preselection based on: Optimize for 4 DM regions cuts Event B-tagging used CERN EP/2002-026 CERN EP/2002-050 Sbottom searches at LEP II • Signature: • Two acoplanar jets (B-Tagging possible) • Missing Energy Backgrounds: Selection based on: 2jets Acoplanarity angle Softness (based on the inv. masses of the jets) Arithm. mean of inv. masses Delphi Aleph

  6. L3 Note 2804 CERN-EP/2003-007 PRELIMINARY CERN EP/2002-050 Stop Searches (three body-decay) Dominant decay mode if kinematically allowed • Signature: • Two acoplanar jets • Acoplanar leptons • Missing Energy DM<10GeV Selection based on: Acoplanarity DM>10GeV was considered as a second case Selection of acoplanar jets with one or more isolated leptons. Min. energy cut on most energetic lepton Similar searches done by: Delphi Aleph Phys. Lett B 499 (2001) 67

  7. If kinematically not allowed and • Flavor changing decay • Loop suppressed CERN-EP/2003-007 CERN-EP/2002-050 L3 Note 2804 Stop Searches (two-body decay) • Signature: • Two acoplanar jets • Missing Energy Similar to • Final selection NN: • 10x10x3 • Input: • Softness, acopl., acolin., b-tag prob. • Sum Fox-Wolfram moments, polar angle of miss momentum Sequential cut approach to search for nearly degenerated and LSP Events forced into 2 jets Preselection based on: DM ranges considered: 5-20GeV and DM>20GeV analysis also performed by: L3 OPAL Aleph Phys. Lett B 499 (2001) 67

  8. Summary of (two/three-body decays) Following mass limits have been obtained Branching Ratio can be 100%, if chargino is purely wino state Z decoupled Numbers given in this table are as submitted to this conference Max coupling

  9. Four-body decay topologies • b jets • jets • leptons • missing mass • missing energy CERN EP/2002-026 Submitted Phys. Letters B Stop Searches (four body decay) [I] Can be substantially enhanced for chargino masses not much larger than current limits mediated by: Virtual chargino + W Virtual chargino + sfermion Use new multi-jet analysis

  10. Multi-jet analysis with taken in 2000 later extended to CERN EP/2002-026 Submitted Phys. Letters B Stop Searches (four body decay) [II] Combined multi-jet and acoplanar jets analysis Branching ratio independent exclusion Hypothesis dominant decay

  11. Width of decay proportional to Phys. Lett B 488(2000) 234 Stop Search (small DM Region) 2-body decay Stop lifetime becomes sizeable for DM small enough Long lived hadron analysis 95%C.L. on stop mass for any tanb

  12. Tevatron Strong produced SUSY Stop and Sbottom at the Tevatron CDF D0 Centre-of-mass energies Run I 1992-1995 ~110 pb-1 used for analysis Run II 2001-2005 ~200 pb-1 currently recorded

  13. Search for Stop with OS Dileptons [I] PRL 90, 25180 (2003) / / ET ET Run I, 107 pb-1 Signature: ≥2 OS leptons, ≥1 jet, Background: Drell-Yan + Jets Heavy Flavor Production t t , Dibosons, Fake Leptons Preselection stage: 2 isolated leptons (e,μ) pT(l1)≥10 GeV, pT(l2)≥6 GeV ≥ 15 GeV Jet ET ≥ 15 GeV ¯ • Data agree w/SM expectations • Sensitivity too low at this stage

  14. Search for Stop with OS Dileptons [II] PRL 90, 25180 (2003) / ET Performed two “blind” analyses: > 35 GeV & Angle Cuts & for small DM, pT(l2) ≥ 6 GeV & for large DM, pT(l2) ≥ 10 GeV Results Excluded new regions of phase space Increased stop sensitivity 4x

  15. hep-ex/0305010 Stop in R-parity violating Decay • RP conservation is not required by SUSY but often build in Run I, 106 pb-1 Signature: ≥1 lepton (e, μ) hadronic t ≥2 b-jets (no tag) Background: Event selection: hadronic t

  16. Search for long lived Stop • Previously searched for: • - Stop decaying within detector • If Stop long lived: • - acts as Min. Ion. Particle • - has a large Time Of Flight • Heavy Stop: • - high pT tracks • - would reach muon system • Selection: • - tracks with pT ≥ 40 GeV/c2 • |TOF-t0| ≥ 2.5 ns Observed 7 events Expected 2.9±0.7(stat) ±3.1(syst) Excluded m(stop)<107 GeV

  17. / / / ET ET ET Sbottoms from Gluino decays [I] • Gluino pair production cross section large • Very distinctive signature Run II, 38.4 pb-1 Signature: 4 bjets, Background: bb QCD t t, W/Z+jets Preselection cuts: ≥ 3 jets, (10GeV,|h|<2) > 35 GeV Lepton veto Df( ,jets) cuts _ _

  18. Assuming / ET Sbottoms from Gluino decays [II] Secondary vertex tagging algorithm used to reduce backgrounds Signal Region: > 50 GeV 1 b-tag 2 b-tags

  19. Conclusions • Interesting results from LEP still come out • D0 and CDF are coming up to speed • Tevatron has the best SUSY discovery potential before LHC /