LEP Search for Single Top production and new fermions Mario Antonelli LNF-INFN Frascati ICHEP 2002 Amsterdam on behalf of the 4- LEP experiments
All limits are at 95 % CL and preliminary The LEP e + e - collider 88-95`89-`95 ~ ,136 `95,`9 ~10 161,172 `96 ~10, ~ `97 ~ `98 ~ ,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
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 ( fb) Suppressed by loop + GIM Extensions of SM could lead to enhancement of such transitions
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
Top decays rapidly via ( 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
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 fb (WW,qq) fb (WW)
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 Limits on FCNC couplings ADLO About 0.55 fb -1 per experiment
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 Limits on branching ratios About 0.55 fb -1 per experiment ADLO
and beyond New fundamental particles ? Substructures ? Fermions in SM Sequential, vector, mirror Isosinglet neutrino Search for excited and heavy fermions Excited Leptons Heavy quarks
VectorSequential Search for heavy fermions F F _ Production: Decay*: *decay to W favored these energies UU NEW Could be sizeable if : UeUe
Heavy leptons Jets and leptons * Bkg* ~ 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
Decay ModeModel DiracMajorana Sequential Vector Mirror Sequential Vector Mirror Sequential Vector Mirror Lower mass limits Decay Mode Stable 102.6
limits M N < 3 GeV 3 < M N < 80 GeV
Search for bjets NEW + clean signature - BR (ZZ->llvv) ~4% - large background + BR (ZZ->qqvv) ~28% simple cut analysis shape analysis
Search for NEW efficiency ~50% (x 4%) ~40% (x 28%) for M b’ =100 GeV background ~ 8 ~665 data 95(exp) 0.8 pb 0.29 pb 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
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
Photons, Leptons and photons Search for pair produced excited leptons Mass reach up to s/2 Topologies: as heavy leptons + f = f ´ f = -f ‘ f = f ´
Single production Mass reach extended up to ~ s Many topologies: radiative CC NC Typical efficiency: 15% ( W ) – 60% ( )
Combined LEP results LEPEXOTICA WG e*
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.
4 jets and missing energy Anomalous ionization loss
Combined LEP results