1. 11 May 2004Nijmegen Colloquium1 Highlights from the LEP e + e – collider Jan Timmermans / NIKHEF Amsterdam

2. 11 May 2004Nijmegen Colloquium2

3. 11 May 2004Nijmegen Colloquium3

4. 11 May 2004Nijmegen Colloquium4 First study B. Richter 1976: C~43 km, E=2*100 GeV, L=10 32 cm -2 s -1, 8 ip’s Les Houches study 1979: study of Z prod. and decay study of WW production Higgs search searches for new leptons, quarks 3 and 4 jet structures, scaling violations 1983: C=27 km; start construction

5. 11 May 2004Nijmegen Colloquium5 Particles in the Standard Model Fermions (matter particles) leptons quarks Gauge bosons , Z, W ± (electroweak interaction) gluons g (strong interaction) Higgs boson H (resulting from EW symmetry breaking) E.g. decays: Z   +  -, Z  bb, W +  e + e, W +  cs

6. 11 May 2004Nijmegen Colloquium6 Some events at LEP1 e + e –  2-fermions Z   +  – Z  e + e –

7. 11 May 2004Nijmegen Colloquium7 Z   +  – Z  q q

8. 11 May 2004Nijmegen Colloquium8 3 jets: Z  q q g (2 quarks and gluon)

9. 11 May 2004Nijmegen Colloquium9 And some events at LEP2 e + e –  4-fermions The first WW event! 1996:  s = 161 GeV e + e –  W + W –  q 1 q 2 q 3 q 4

10. 11 May 2004Nijmegen Colloquium10 e + e –  ZZ   +  – qqe + e –  Z *  *   +  – e + e –

11. 11 May 2004Nijmegen Colloquium11  events/experiment:  4.5 M Z events  10000 WW events  600 ZZ events  250 single-W events  LEP1 (1989-1995): ~200 pb -1 /exp LEP2 (1996-2000): ~700 pb -1 /exp

12. 11 May 2004Nijmegen Colloquium12 Z line shape and asymmetries e+e+ e-e- f f Z e+e+ e-e- f f  pole cross-section: partial width: total width: vector and axial- vector couplings

13. 11 May 2004Nijmegen Colloquium13 Forward-backward asymmetry: At the Z pole: Measure lepton partial width  ll and F/B asymmetry A FB gives the couplings g Vl and g Al (for l=e, ,  ) Effective weak mixing angle: Effective couplings contain radiative corrections, which depend on the top quark mass and Higgs boson mass

14. 11 May 2004Nijmegen Colloquium14 Some examples of radiative corrections: e+e+ e-e- b b  /Z/Z t t W e+e+ e-e- f f Z H e+e+ e-e- f f t t Higgs loop top quark loop W loop

15. 11 May 2004Nijmegen Colloquium15 Z line shape Moriond 1990: m Z = 91171 ± 12 ± 32 (incl.  E LEP ) MeV  Z = 2538 ± 26 ± 28 MeV N = 3.04 ± 0.12 first evidence 3 generations Now: m Z = 91187.5 ± 2.1 MeV  Z = 2495.2 ± 2.3 MeV N = 2.9841 ± 0.0083

16. 11 May 2004Nijmegen Colloquium16 Beam energy precision  0.2 MeV from resonant depolarisation But corrections needed due to: TIDES LEVEL LAKE TGV

17. 11 May 2004Nijmegen Colloquium17 Axial and Vector couplings for leptons Measured from partial widths  ll,, forward-backward asymmetries A FB 0,l and τ polarisation g Vf / g Af = 1 – 4 | Q f | sin 2  eff f Couplings and lepton-universality established at 1 per-mille (g Al ) and few % (g Vl )

18. 11 May 2004Nijmegen Colloquium18 Vertex Detectors: Precise  -lepton & b-quark studies Here DELPHI LEP2 version

19. 11 May 2004Nijmegen Colloquium19 R b =  b /  had and top quark mass Summer 1992:  b = 373  9 MeV  I 3 b = -1/2 (370 MeV; for I 3 b =0: 24 MeV)  Top quark must exist R b is also sensitive to top quark mass, but much less than sin 2  eff ! lept

20. 11 May 2004Nijmegen Colloquium20 Top mass: predicted by LEP Prediction m top from EW fit EPS93 Marseille: m top = 166 –19 -22 GeV ICHEP94 Glasgow: m top = 178 -11 -19 GeV and CDF saw excess due to top at m top = 174 -10 -23 GeV EPS95 Brussels: both CDF and D0 observed top at predicted mass. +17 +19 +11 +18 +10 +13 Great success for the Standard Model

21. 11 May 2004Nijmegen Colloquium21 Two most precise sin 2  eff values from SLD A LR and LEP A 0,b differ by 2.9  lept FB SM: 0.1036 A 0,b (and also A 0,c ) prefer a high value for the Higgs boson mass FB A puzzle left ….. : comparison sin 2  eff lept

22. 11 May 2004Nijmegen Colloquium22  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 at few per-mille, thanks to high-precision Si vertex detectors

23. 11 May 2004Nijmegen Colloquium23 B s oscillations: to be discovered at Tevatron  m s > 14.4 ps -1 at 95% C.L. Continuous improvements in analysis techniques

24. 11 May 2004Nijmegen Colloquium24 CKM matrix Quark mass eigenstates are not the same as the weak eigenstates. The Cabibo-Kobayashi-Maskawa matrix relates these two bases.  unitarity triangle

25. 11 May 2004Nijmegen Colloquium25 B physics and CKM matrix In excellent agreement with sin2  measurements from BaBar/Belle |V td | from B d 0 – B d 0 oscillations |V ts | from B s 0 - B s 0 oscillations |V cb | from semileptonic b  cl transitions |V ub | from semileptonic b  ul transitions

26. 11 May 2004Nijmegen Colloquium26 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 C F, C A, T F T F / C F

27. 11 May 2004Nijmegen Colloquium27 QCD: running of  s Results from fits to different event shape variables. Combined fit at all energies:  s (M Z ) = 0.1201  0.0003  0.0009  0.0047 (stat) (exp.syst) (theor.hadr.) (theor.ev. shapes)

28. 11 May 2004Nijmegen Colloquium28 only exchange No ZWW vertex WW cross section Clear evidence for the SU(2) x U(1) Gauge structure Exp. Errors 1-3% / energy point CC03 diagrams: Theory predictions include full O(  em ) corrections; theory error  0.5%

29. 11 May 2004Nijmegen Colloquium29 Single W WW  DLO Quartic Gauge Couplings

30. 11 May 2004Nijmegen Colloquium30 W mass measurement M w 2  1 – ––––   ––––  1 –  r  Mw2Mw2 MZ2MZ2  GF 2GF 2 WW t b W WW H  M w  ln M H  M w  M t 2 W mass defined by relativistic Breit-Wigner lineshape of the W propagator with s-dependent width   M top  M W Direct 4 GeV34 MeV Indirect10 GeV33 MeV precision M W measurement 0.04% gives handle on Higgs mass

31. 11 May 2004Nijmegen Colloquium31 W mass W masses reconstructed directly from the decay products Constrained fits improve mass resolution from  8 GeV to  3 GeV before 4C fit after 4C fit qqqq qq  qq  qqe

32. 11 May 2004Nijmegen Colloquium32 W mass: LEP combined results Not yet FINAL Working on systematics, mainly in 4q Apart from NuTeV result (from rates of CC and NC (anti-) scattering) very good agreement between direct and indirect measurements NEW

33. 11 May 2004Nijmegen Colloquium33 We searched….. and searched….. No Higgses, 4 th -generation, sleptons, squarks, charginos, neutralinos.... Large part of the MSSM parameter space excluded

34. 11 May 2004Nijmegen Colloquium34 SM Higgs search Higgs strahlung: dominantWW fusion: small (can go beyond ‘kinematical limit’) Branching ratios (m H =115 GeV): H  bb (74%) H   (8%) H  WW (8%) Final states: bbqq (4-jet channel) bb (missing energy channel) bbee, bb  (leptonic channel) bb ,  bb (tau channel) Selections: cut based or NN select multi-hadronic events look for b-tagged jets lepton identification apply constraint fits + sometimes W/Z mass constraints

35. 11 May 2004Nijmegen Colloquium35

36. 11 May 2004Nijmegen Colloquium36 Mass distributions: But not only mass information useful! Combine all information in a discriminating variable (event likelihood or NN output) 2-dim inputs to statistical analysis: - invariant mass of bb jet combination - discriminating variable (containing b-tags, kinematics, jet-properties)

37. 11 May 2004Nijmegen Colloquium37 CL s+b 1-CL b Likelihood test: sig+bkg  bkg 1-CL b measures incompatibility with bkg CL s+b a measure of compatiblity with s+b

38. 11 May 2004Nijmegen Colloquium38 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 CL s = CL s+b / CL b when CL s < 0.05 the hypothesis is rejected at 95% CL  M H > 114.4 GeV (115.3 expected) FINAL 2003

39. 11 May 2004Nijmegen Colloquium39 Global electroweak fit Results of different fits: using only Z pole data using all data

40. 11 May 2004Nijmegen Colloquium40 Very good consistency between direct and indirect measurement of m t and m W Both prefer low Higgs boson mass m H < 237 GeV at 95% CL (no big effect from NuTeV)

41. 11 May 2004Nijmegen Colloquium41 Conclusions  LEP was great!  Full gauge structure of the SM has been measured, and many measurements in good agreement with the SM prediction  Largest discrepancy between A b FB (LEP) and A LR (SLD) at 3  but much less w.r.t. average in terms of sin 2  eff !  SM Higgs boson not yet found: M H > 114.4 GeV A task for the Large Hadron Collider experiments lept  total output: ~ 300 journal papers/experiment  PhD theses in NL: 14 DELPHI, 35 L3 (of which 22 KUN)

42. 11 May 2004Nijmegen Colloquium42 Backup slides

43. 11 May 2004Nijmegen Colloquium43 Results of different fits: using only Z pole data using all data using all data but NuTeV Global electroweak fit

44. 11 May 2004Nijmegen Colloquium44 Very good consistency between direct and indirect measurement of m t and m W Both prefer low Higgs boson mass m H < 219 GeV at 95% CL (no big effect from NuTeV) Summer 2003

45. 11 May 2004Nijmegen Colloquium45

46. 11 May 2004Nijmegen Colloquium46 We searched….. and searched….. But sometimes…… No Higgses, 4 th -generation, sleptons, squarks, charginos, neutralinos.... Large part of the MSSM parameter space excluded

47. 11 May 2004Nijmegen Colloquium47 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% ALEPH Why it is good to have more than one expt.