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Combination of the LEPII  f f and γγ Results and Searches for N ew Phenomena

Combination of the LEPII  f f and γγ Results and Searches for N ew Phenomena. Dimitri Bourilkov University of Florida for the LEP Electroweak WG DPF 2002, Williamsburg, VA, USA May 24, 2002. Falling signal, increasing backgrounds (two-photon, W + W - , ZZ …)

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Combination of the LEPII  f f and γγ Results and Searches for N ew Phenomena

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  1. Combination of the LEPIIf f and γγ Results and Searches for New Phenomena Dimitri Bourilkov University of Florida for the LEP Electroweak WG DPF 2002, Williamsburg, VA, USA May 24, 2002

  2. Falling signal, increasing backgrounds (two-photon, W+W-, ZZ …) Initial state radiation  select high s’ events – ambiguity due to interference ISR/FSR LEP2 Monte Carlo Workshop, hep-ph/0007180, CERN-YR-2000-009 Fermion-pair production DPF 2002

  3. Photon-pair Production DPF 2002

  4. LEP2f f and γγ Groups Combine the measurements of LEP2 data: 720 pb-1/exp @ 130-208 GeV (> 190 GeV preliminary) • Total and differential cross sections (f f and γγ ) • Forward-backward asymmetries (μ+μ- and τ+τ-) • Heavy flavors: Rb and Rc, , Afb • Test the SM at % level and constrain tightly current / future extensions • New results: e+e- and γγ (hep-ex/0112021, LEP2FF/02-01) Web page: http://lepewwg.web.cern.ch/LEPEWWG/lep2 DPF 2002

  5. Combination of LEP2 Data • Concentrate on non-radiative samples  highest energy / sensitivity to new physics – probe higher scales than direct searches at same s • Correct data before averaging  common signal definition • Correlations obtain full error matrices after averaging – 5 classes of systematic errors: • Uncorrelated • Correlated between: energies, channels, energies & experiments, energies & experiments & channels Correlations important! E.g. e+e- , hadrons: O(25%) DPF 2002

  6. Fermion Pairs Averaged over s: h/ h < 1 % (theory 0.3 %);  Afb ~ 0.01 Good agreement with SM – hadronic 1.8 s.d. excess averaged over all s DPF 2002

  7. Averaged over s: (/ )forward ~ 1 % (theory ~ 0.5%) (/ )central ~ 1.5 % (theory ~ 1.5%) Expected sensitivity: Contact interactions scale > 20 TeV (VV) hep-ph/0007180 Extra dimensions scale > 1.2 TeVhep-ph/0103039 (1999: scale Ms > 1.1 TeV from combined analysis of 183-189 GeV data: JHEP 08(1999)006 ) d/dcos e+e- DPF 2002

  8. d/dcosμ+μ- and τ+τ- DPF 2002

  9. Heavy Flavors Averaged over s: Rb/Rb ~ 2.5 % ;  Afbbb ~ 0.06 DPF 2002

  10. general framework for new int.: scale   s coupling g (convention g2 = 4) operators with canonical dimension N > 4  coupling 1/MN-4 |ij| < 1 helicity amplitudes Contact Interactions DPF 2002

  11. 95% confidence limits for μ+μ- and τ+τ- :  > 8.5 – 26.2 TeV Assume only 1 flavor active > 2.2 – 14.6 TeV bb  > 1.4 – 7.4 TeV cc Contact Interactions DPF 2002

  12. Z’ Bosons • New neutral, heavy boson Z’ • Couplings of Z’ tof f model dependent • Z and Z’ can mix  mixing angle ZZ’(from LEP1 mixing is very small; take 0) LEP2 limits @ 95 % CL Model    LR SSM MZ’ (GeV) 678 463 436 800 1890 DPF 2002

  13. γγ (/ )~ 1.2 % (theory ~ 1 %) + > 365 GeV - > 379 GeV Ms > 0.96 TeV DPF 2002

  14. Conclusions • SM describes the full set of precise LEP2 measurements @ 130-208 GeV (results above 190 GeV preliminary) • No hint for new phenomena … in spite of sensitive searches! • Many new combined limits @ TeV scale (CI, Z’) obtained OR in the pipeline (extra dimensions, sneutrinos, leptoquarks …) • Combine final measurements, provide a reference point in the era after LEP & constrain tightly physics beyond the SM DPF 2002

  15. Outlook The Standard Model rules at 200 GeV … looking forward to 2 TeV ! DPF 2002

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