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

3. All limits are at 95 % CL and preliminary The LEP e + e - collider 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 E CM (GeV) Year High centre of mass energy + Luminosity + clean experimental environment

4. Search for single top production via FCNC At tree level SM, there are no vertices for these FCNC processes (GIM mechanism V CKM =V CKM -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

5. The FCNC vertices tqV (V = ,Z) probed in Existing limits HERA: Sensitivity to tu  coupling  K ut  ZEUS: SM: TEVATRON: CDF: rare decays of top quark top-q associated production very weak constraint: N tt ~10 2 Using the following vertices CDF upper limits on BR translate  corresponding to CDF limits   CDF (200,174) < 0.85 pb 174 179 169

6. Top decays rapidly via (10 -24 sec) no top hadrons formed c-jet b-jet Topologies E t ~ m t E W ~ (m t 2 +m W 2 -m b 2 )/2m t E b ~ (m t 2 -m W 2 +m b 2 )/2m t E q ~  s - m t Kinematics at 189 GeV c-jet b-jet W-jet

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

8. Combined * LEP results *LR method for combination LEPEXOTICA WG Cross section upper limits for m t =174 GeV GeV  95(obs) pb  95(exp) pb 1890.11 1920.380.33 1960.360.20 2000.21 2020.300.35 2050.200.25 2070.170.18 Limits on FCNC couplings ADLO About 0.55 fb -1 per experiment

9. Combined * LEP results *LR method for combination LEPEXOTICA WG Cross section upper limits for m t =174 GeV GeV  95(obs) pb  95(exp) pb 1890.11 1920.380.33 1960.360.20 2000.21 2020.300.35 2050.200.25 2070.170.18 Limits on branching ratios About 0.55 fb -1 per experiment ADLO

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

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

12. Heavy leptons Jets and leptons * Bkg* ~ 0.3-1 pb E miss + P tmiss  ~ 35-15% J-L Candidates in agreement with SM expectation depending on (5%) Heavy stable charged particles Small U and HSCP 65% 0.01 pb decay length:   U -2 M L -6

13. Decay ModeModel DiracMajorana Sequential Vector Mirror 101.3 102.6 100.8 89.5 ----- 89.5 Sequential Vector Mirror 101.5 102.7 101.0 90.7 ----- 90.7 Sequential Vector Mirror 90.3 99.3 90.3 80.5 ----- 80.5 Lower mass limits Decay Mode 100.8 101.2 100.5 101.9 102.1 101.9 Stable 102.6

14. limits M N < 3 GeV 3 < M N < 80 GeV

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

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

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

18. Photons, Leptons and photons Search for pair produced excited leptons Mass reach up to  s/2 Topologies: as heavy leptons + f = f ´103.0103.1102.2102.0102.4 95.3 f = -f ‘ 98.0 102.7102.8 f = f ´102.9 102.8

19. Single production Mass reach extended up to ~  s Many topologies: radiative CC NC Typical efficiency: 15% (  W ) – 60% (  )

20. Combined LEP results LEPEXOTICA WG e*

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

22. 4 jets and missing energy Anomalous ionization loss

23. Combined LEP results