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LEP programme Final report Peter Kluit

LEP programme Final report Peter Kluit. Thanks to: Wes Metzger, Jan Timmermans and my LEP collegues. LEP construction. DELPHI. L3. First study B. Richter 1976 C~43 km, E=2*100 GeV, L=10 32 cm -2 s -1 , 8 interaction points Les Houches study 1979 study of Z production and decay

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LEP programme Final report Peter Kluit

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  1. LEP programme Final reportPeter Kluit Thanks to: Wes Metzger, Jan Timmermans and my LEP collegues SAC presentation

  2. LEP construction SAC presentation

  3. DELPHI L3 SAC presentation

  4. First study B. Richter 1976 • C~43 km, E=2*100 GeV, L=1032 cm-2s-1, 8 interaction points • Les Houches study 1979 • study of Z production and decay • study of WW production • Higgs search • searches for new leptons, quarks • 3 and 4 jet structures • Start construction1983: C=27 km • NIKHEF joins DELPHI & L3 SAC presentation

  5. LEP1 (1989-1995): ~200 pb-1/exp LEP2 (1996-2000): ~700 pb-1/exp • Events/experiment:  4.5 M Z events LEP1 •  10000 WW events •  600 ZZ events •  250 single-W events LEP2 SAC presentation

  6. Z line shape Moriond 1990: mZ = 91171 ± 12 ± 32 (incl. ELEP) MeV Z = 2538 ± 26 ± 28 MeV N = 3.04 ± 0.12 First evidence 3 generations Now status up to end 2003: mZ = 91187.5 ± 2.1 MeV Z = 2495.2 ± 2.3 MeV N = 2.9841 ± 0.0083 One of the main LEP results SAC presentation

  7. Beam energy precision 0.2 MeV from resonant depolarisation But corrections needed due to: TIDES LEVEL LAKE TGV SAC presentation

  8. Vertex Detectors: Precise -lepton b-quark studies here the DELPHI LEP2 vertex detector SAC presentation

  9. Now (end 2003): Rb determined with 0.3% Rb = b / had and top quark mass • Summer 1992: • b = 3739 MeV  I3b = -1/2 • (370 MeV; for I3b =0: 24 MeV) • Top quark must exist Rb is also sensitive to top quark mass, but much less than sin2qeff ! SAC presentation

  10. Prediction mtop from EW fit EPS93 Marseille: mtop = 166 –19 -22 GeV ICHEP94 Glasgow: mtop = 178 -11 -19 GeV and CDF saw excess due to top at mtop = 174 -10 -23 GeV EPS95 Brussels: both CDF and D0 observed top at predicted mass. +17 +19 +11 +18 +10 +13 Top mass: predicted by LEP Great success Standard Model (Nobel prizes for ‘t Hooft and Veltman) SAC presentation

  11. lept A puzzle left ….. : comparison sin2qeff SM: 0.1036 Two most precise sin2eff values from SLD ALR and LEP A0,b differ by 2.9 lept A0,b (and also A0,c ) prefer a high value for the Higgs boson mass FB FB FB SAC presentation

  12.  lepton: a puzzle solved • lifetime related to  lifetime,  mass,  mass and leptonic  branching ratio Up to 1992 a 2-2.3  discrepancy between the coupling constants g and g In 1992 a new, more precise  mass by BES Now - -e universality tested at few per-mille, thanks to high precision vertex detectors SAC presentation

  13. Bs oscillations: to be discovered Bd oscillations discovered at LEP Continuous improvements in analysis techniques ms > 14.4 ps-1 at 95% C.L. SAC presentation

  14. |Vtd| from Bd0 – Bd0 oscillations • |Vts| from Bs0 - Bs0 oscillations • |Vcb| from semileptonic bcl transitions • |Vub| from semileptonic bul transitions B physics and CKM matrix Excellent agreement with sin2bfrom BaBar/Belle Profound test of SM charged current sector SAC presentation

  15. TF / CF QCD: test of gluon selfcoupling From fit to angular distributions in 4-jet events. Rel. strength of couplings qqg, ggg, gqq depends on gauge group through Casimir factors CF , CA , TF SAC presentation

  16. QCD: running of s Results from fits to different event shape variables. Combined fit at all energies: s(MZ) = 0.1201  0.0003  0.0009  0.0009  0.0047 (Note this year Nobel Prize) (stat) (exp.syst) (theor.hadr.) (theor.ev.shapes) SAC presentation

  17. only  exchange No ZWW vertex WW cross section CC03 diagrams: TripleGauge Coupling Theory predictions include full O(aem) corrections; theory error  0.5% Clear evidence for the SU(2) x U(1) Gauge structure SAC presentation

  18. DLO Single W WW Quartic Gauge Couplings SAC presentation

  19. qq qqqq before 4C fit qqe qq after 4C fit W mass reconstruction • Reconstructed directly from the decay products • Constrained fits improve mass • resolution from 8 GeV to 3 GeV SAC presentation

  20. W mass: LEP combined results (end 2003) • Not yet final • Working on systematics, mainly in 4q Apart from NuTeV result ( scattering) Very good agreement between direct and indirect measurements SAC presentation

  21. No Higgses, 4th-generation, sleptons, squarks, charginos, neutralinos.... Large part of the MSSM parameter space excluded We searched….. and searched….. and searched….. and searched….. and searched….. But sometimes…… SAC presentation

  22. ALEPH Why it is good to have more than one experiment • 1995: 130-136 GeV • 4-jet events • Sum of di-jet masses • with smallest M • 16 events (8.3 exptd) • Prob. accumulation in 6.3 GeV bin: 0.01% SAC presentation

  23. Higgs strahlung: dominant WW fusion: small (can go beyond ‘kinematical limit’) SM Higgs search • Final states: (Higgs to bb or ) • bbqq (4-jet channel) • bb (missing energy channel) • bbee, bb (leptonic channel) • bb, bb (tau channel) SAC presentation

  24. ALEPH Higgs candidate SAC presentation

  25. Final LEP Higss search results • Small excess around 116 GeV but less than 2 (mainly coming from ALEPH candidates and from four-jet events) • Excess was 2.9 on 3/11/2000 • CLs = CLs+b / CLb • when CLs < 0.05 the hypothesis is rejected at 95% CL Lower limit on Higgs mass MH > 114.4 GeV (115.3 expected) SAC presentation

  26. Results of different fits: • using only Z pole data • using all data • using all data but NuTeV Global electroweak fit SAC presentation

  27. Good consistency between direct and indirect measurement of mt and mW • Both prefer low Higgs boson mass mH < 219 GeV at 95% CL Light Higgs to be discovered at LHC SAC presentation

  28. LEP was great! • Full gauge structure of the SM has been measured, and many measurements in good agreement with the SM prediction • Fantastic precision measurements of W and Z boson, b quark and lepton properties, including the CKM matrix • SM Higgs boson not yet found: MH > 114.4 GeV • NIKHEF was involved in many important analyses: • total output: ~ 300 journal papers/experiment • PhD theses: 14 DELPHI, 35 L3 (of which 22 KUN) • Papers still to come: ~55 DELPHI and ~20 L3 Conclusions SAC presentation

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