1. Precision electroweak physics Roberto Tenchini INFN-Pisa 5th Rencontres du Vietnam Particle Physics and Astrophysics Hanoi August 5 to August 11, 2004

2. 21 Years of W and Z Physics 1986 UA1 UA2 1990 UA2 CDF 2000 TeV LEP  =1.5 GeV  =400 MeV  =100 MeV  =39 MeV Only Published Results (*) Preliminary average 2004 :  =34 MeV, weight of LEP 2/3, Tevatron 1/3 (*)

3. 21 Years of W and Z Physics 1986 UA1 UA2 1990 LEP  =1.7 GeV  =31 MeV Only Published Results  =2.1 MeV

4. 21 Years of W and Z Physics E.W. Tree level SM relation Strong Evidence of pure E.W. Higher Order Corrections 19862002 19862002 (with running  QED)

5. Tree level not enough : more parameters Radiative corrections in function of three more parameters M top, M higgs,  s An Observable is written as Example : one loop radiative corrections

6. Outlook of the rest of the talk Z Couplings: asymmetries at the Z and measurement of sin 2 (  ) W –(a crisis ?) W Couplings: W Branching Ratios –(three LEP exp are final) Measurement of the W mass –(some hot issues) Constraints on the SM Higgs NEW MEANS FIRST TIME AT THIS CONFERENCE

7. Asymmetries at the Z pole Z decay into a ff pair. With unpolarized beam from fermion direction and helicity 3 asymmetries Can measure for e, , ,c,b Can measure with  ’s Z with beam polarization (SLC) :

8. Electroweak Couplings : from deep inelastic scattering to LEP-SLC Huge increase in precision

9. Asymmetries at the Z and Consistency is at 6.2% Long standing difference between Alr and A FB (b) NEW FINAL

10. b anomalous couplings ? No independent evidence measures Plots like this one include b asymmetry ! NEW FINAL

11. Again on the b asymmetry Two techniques use semileptonic b decays use weighted charge of particles in the hemisphere Very different systematic effects LEP average still statistically dominated Example: Stability of result as a function of the b purity NEW FINAL

12. The b asymmetry: results LEP average Leptons only Inclusive NEW FINAL

13. My conclusion on “sin 2 (  ) crisis” There is no evidence of problems related to the b asymmetry measurement Will solve the A LR -b asymmmetry discrepancy with future linear colliders if –Polarization of both beams available –Very high statistics run at the Z will take place

14. WW Production at LEP2 Three diagrams contribute at Born level (CC03 diagrams) : Actually look for subsequent W decay into lepton-(anti) neutrino and quark 1 - (anti) quark 2. Real process is defined by exp. cuts

15. WW production at LEP2: the backgrounds Selections needed to Extract events from background Classify WW decays to different channels (fully hadronic, fully leptonic, semileptonics) (Semi)leptonic decays can further be separated in e, ,  channels

16. Event selection q q q q q q Semileptonic (qq l ) Hadronic (4q) Leptonic 11%44%45% Lepton=e, , 

17. Cross Sections in all channels N j selected events in each selection (j) L total luminosity  j expected events function of  i WW for each channel (i)  ij efficiency matrix  j bkg background cross section  j 4f four fermion interference correction Likelihood EXAMPLE OF PROCEDURE

18. Four Fermion Interference Small Correction taken from Monte Carlo (~ 1% relative) SIGNAL (following the CC03 definition) Single W Most important(*) 4-f (non WW) processes can be directly measured (*) for the interference

19. Total WW Cross Section Precision reached by LEP experiments a challenge to theoretical predictions –Predictions with enhanced O(  ) radiative corrections are needed ! Strong evidence of Triple Gauge Couplings NEW 3 exp FINAL

20. W decays : Branching Ratios Standard Model : 10.8% Standard Model : 67.5% Test of lepton universality:  result higher than e+  NEW ADL FINAL

21. W Leptonic Couplings NEW ADL FINAL If electron and muon couplings are assumed to be the same and combined the  result is 3  higher was 2.3  in summer 2003 is 2.6  if final results only are used

22. W Mass at LEP from direct reconstruction Above threshold the W mass is measured from direct reconstruction of the jet-jet invariant mass in the fully hadronic and semileptonic channels Event reconstructed as 2 (semileptonic candidate) or 4 (hadronic candidate) jets with iterative procedure In the hadronic channel 3 jet-jet combinations from 4 jet WW boson pairs at LEP –161 – 209 GeV centre of mass energy –~700 pb -1 by each experiments –~4500 qqqq, ~4000 l qq events for each experiments.

23. LEP2 EnergySystematics: At LEP2: –  E beam ~20MeV (  E/E~10 -4 )   m W ~17MeV –Error coming mainly from extrapolation. Resonant depolarization Resonant depolarization: –only works up to 60GeV  extrapolation Kinematic fit imposing energy-momentum conservation  RECENT FINAL

24. Reconstructed M W L3  qq DELPHI e qq OPAL  qq  qq

25. LEP: Systematic Uncertainties for M W QED effects (ISR, FSR, etc.) Fragmentation Detector effects Uncertainty on the LEP beam energy Colour Reconnection Bose-Einstein correlations (Weight of qqqq in LEP combination: 0.09) Effort to reduce this error by designing 4q analyses less affected by CR effects

26. Final State Interactions Separation of W decays vertex at LEP2 ~0.1 fm  small with respect to the hadronization scale ~1fm Interconnection phenomena : Final State is no longer factorized into two separated W’s  can bias the W mass in the fully hadronic channel NEED DATA to control these non-perturbative effects

27. Present LEP result: Colour Reconnection constrained by the particle flow analysis Most CR models predict a modified particle flow in W + W - events: CR:No CR: W-W- W+W+ W-W- W+W+ The ratio of particle flow between the inter and intra-W regions is built: (A + B) / (C + D) A B C D Data -SK1(extreme parameter) -Jetset Measurement sensitive only to extreme scenarios, Colour Reconnection Systematic error ~ 90 MeV

28. Final LEP result: Colour Rec. constrained by Mass variation when soft particles are excluded Mass Shift predicted by model Example: difference between Mass measured in standard analysis and Mass measured using only particles in the core of the jet Models This correlation is a general feature of All Models : CR is expected to affect mainly –low momentum particles –particles away from the jet core By studying Mass Stability (or Measuring the W mass only with particles in the jet core ) expect to reduce CR Systematic Error to ~ 50 MeV

29. mass difference (no FSI syst)  M W (qqqq-l qq)= +22  43 MeV M W at LEP : 4q and l qq 80.411±0.032(stat) ±0.030(syst)GeV/c2 80.420±0.035(stat) ±0.101(syst)GeV/c2

30. Before LEP: measurements at hadron colliders (SppS, Tevatron Run I) After LEP : measurements at hadron colliders (Tevatron Run II, LHC) Drell-Yan single W production (quark-antiquark annihilation) W decay to leptons (e or  ) + neutrino Fit to M W T, the transverse mass distribution W mass from hadron colliders: the past and the near future ! -

31. TeVatron RUN II W and Z cross sections

32. Present M W at LEP and TeVatron

33. ElectroWeak fit results Electroweak theory tested at one loop level Indications for a light Higgs Summer 2003 Winter 2004

34. Conclusions Asymmetries at the Z are final (including quarks) W cross sections at LEP are essentially final The LEP W mass result is still PRELIMINARY –LEP collaborations are still working on this measurement, final results for the end of this year – Activities to reduce the uncertainty due to CR effects and gain information from the 4q channel Reducing the LEP final error (~ 35 MeV ) will be the challenge for Tevatron II and LHC In spite of the increased top mass there is still evidence for a light Higgs

35. Backup Slides

36. Impact parameter Secondary vtx Transverse momentum Momentum A FB (b) from semileptonic decays Can fit independently b and c asymmetries, mixing and background composition

37. A FB (b) QCD corrections : cross-check No evidence of bias due to gluon emission

38. W Leptonic Branching Ratios NEW ADL FINAL If the Branching Ratios to electron and muon are assumed to measure the same quantity and combined the  result is 3  higher was 2.3  in summer 2003 is 2.6  if final results only are used

39. Measuring BE in W + W - events Inter W, BEI confirmed Between W’s, BEB, disfavoured  M W down from ~35 to ~15 MeV Final BEB BEI eg

40. Error on W mass (Run I) Theory improvements Improve PDF constraints with measurements (W charge asymmetry, Z rapidity distribution) These errors are determined using CDF/D ∅ data,scale with luminosity Detector improvements for Run II will also help 40 MeV per experiment with 2 fb -1 feasible

41. Running of  QED:   

42. LEP average: Mw from the threshold method at 161 GeV

43. Kinematic Fits Kinematic fit used to improve reconstructed four momenta

44. Spectrometer Based on measurement of lepton bending angle Spectrometer Based on measurement of lepton bending angle LEP Energy (2) 3 methods used to cross-check extrapolation: Systematics: Radiative return Energy loss Based on the frequency of the field provided to beam to compensate from syncroton radiation. Energy loss Based on the frequency of the field provided to beam to compensate from syncroton radiation. E loss by sync.

46. Jet velocity & mass Last jet reconstruction (with ECAL cleaning) Z peak jets boost (T>0.8) Jet boost (and mass) now well calibrated ! Removing low energy neutrals (<1.5 GeV, and <2 GeV if mixed)

47. Radiative Z peak Systematic uncertainties Unbinned likelihood fit to a pdf built with a fit to the MC reference

49. Forward-backward Asymmetry of The pull of individual pseudo-observables in the global fit Deep Inelastic N scattering Prob(  2 ) 42% 14% Prob(  2 ) 14 % 1.7%

51. Observables vs top and Higgs mass

52. Electroweak observables in the (m top, m higgs ) plane