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LEP Search for Single Top production and new fermions

LEP Search for Single Top production and new fermions. Mario Antonelli LNF-INFN Frascati ICHEP 2002 Amsterdam. on behalf of the 4- LEP experiments. The LEP e + e - collider. E CM (GeV) Year. 88-95 `89-`95 ~ 175 130,136 `95,`9 ~ 10

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LEP Search for Single Top production and new fermions

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  1. LEP Search for Single Top production and new fermions Mario Antonelli LNF-INFN Frascati ICHEP 2002 Amsterdam on behalf of the 4- LEP experiments

  2. The LEP e+e- collider ECM (GeV) Year 88-95 `89-`95 ~175 130,136 `95,`9 ~10 161,172 `96 ~10, ~10 181-184 `97 ~55 189 `98 ~170 192,196,200,202 `99 ~(30,80,80,30) 205 – 208 `00 ~207 >208 ‘00 ~3 High centre of mass energy + Luminosity + clean experimental environment All limits are at 95 % CL and preliminary

  3. Search for single top production via FCNC At tree level SM, there are no vertices for these FCNC processes (GIM mechanism VCKM=VCKM-1). FCNC appear at loop level Very small cross section ( 10-9 fb) Suppressed by loop + GIM Extensions of SM could lead to enhancement of such transitions

  4. s corresponding to CDF limits TEVATRON: Using the following vertices CDF: s95CDF(200,174) <0.85 pb SM: very weak constraint: Ntt~102 169 CDF upper limits on BR translate 174 179 HERA: Sensitivity to tug couplingKutg ZEUS: The FCNC vertices tqV (V = g,Z) probed in • rare decays of top quark • top-q associated production Existing limits

  5. b-jet b-jet Et ~ mt c-jet c-jet EW ~ (mt2+mW2-mb2)/2mt W-jet Eb ~ (mt2-mW2+mb2)/2mt n Kinematics at 189 GeV Eq ~ s - mt l W-jet Topologies Top decays rapidly via (10-24 sec) no top hadrons formed

  6. e 50-200 fb (WW,qq) 10-30 fb (WW) ~ Selections and performances 2 selections: and W decay hadronic Leptonic kinematics + b-tag + lepton id + Emiss OPAL 10%-15% 4%-7% Bkg ~ No excess seen in data

  7. Combined* LEP results LEPEXOTICA WG Limits on FCNC couplings Cross section upper limits for mt =174 GeV ADLO About 0.55 fb-1 per experiment *LR method for combination

  8. Combined* LEP results LEPEXOTICA WG Limits on branching ratios Cross section upper limits for mt =174 GeV ADLO About 0.55 fb-1 per experiment *LR method for combination

  9. Sequential, vector, mirror Isosinglet neutrino Heavy quarks Excited Leptons Search for excited and heavy fermions Fermions in SM and beyond New fundamental particles ? Substructures?

  10. _ F F Sequential Vector Search for heavy fermions Production: Ue Decay*: NEW U Could be sizeable if : *decay to W favored these energies

  11. Emiss +Ptmiss depending on Heavy stable charged particles HSCP J-L e ~ 35-15% (5%) 65% decay length:  bU-2ML-6 Bkg* ~ 0.3-1 pb 0.01 pb Small U and * Heavy leptons Jets and leptons Candidates in agreement with SM expectation

  12. Lower mass limits

  13. limits MN < 3 GeV 3 < MN < 80 GeV

  14. Search for NEW bjets bjets +clean signature - BR (ZZ->llvv) ~4% - large background + BR (ZZ->qqvv) ~28% simple cut analysis shape analysis

  15. Search for NEW Preliminary results about 344 pb-1 at energies above 200 GeV efficiency ~50% (x 4%) ~40% (x 28%) for Mb’=100 GeV background ~ 8 ~665 data 8 599 s95(exp) 0.8 pb 0.29 pb s95 0.65 pb 0.26 pb s95= 95% CL upper limit on Combined: <0.21 pb for Mb’=100 GeV at s=206.6 GeV DELPHI CDF limits(PRL 84 (2000) 835) Mb’=100 GeV: CDF

  16. _ l* l* Search for excited leptons Substructure at a scale Lexcited leptons l* l Prompt decay: f, f’ control strength of SU(2), U(1) couplings single production Pair production Virtual contribution l* l e*,ne* e*,ne* e,ne

  17. Search for pair produced excited leptons Mass reach up to s/2 Topologies: as heavy leptons + Photons, Leptons and photons

  18. Single production Mass reach extended up to ~s Many topologies: radiative CC NC Typical efficiency: 15% (tW ) – 60% (mg)

  19. e* Combined LEP results LEPEXOTICA WG

  20. Conclusion LEP is (was) beautifull: centre-of-mass energies and luminosities above the specifications. New physics thoroughly searched for with the 2.5 fb-1 luminosity collected at LEP at Ecm up to 209 GeV Numbers and properties of the events selected generally in agreement with SM expectation Experimental constrains are dramatically improved. We look forward to the near(?) future

  21. 4 jets and missing energy Anomalous ionization loss

  22. Combined LEP results

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