SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 1 Direct and Indirect Probes of EWSB in e + e - Annihilation (LEP and SLC) Higgs Outline : Patrick Janot, CERN First Lecture: Second Lecture: Third Lecture: EP (and SLC too! )

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 2 Indirect Probes of EWSB at LEP and SLC Z W H m W =m Z cos W Common Goals of LEP and SLC:  Check the internal consistency of the Standard Model of Electroweak the Standard Model of Electroweak interactions (Z & W studies); interactions (Z & W studies);  Test with precision the predictions of Electroweak Symmetry Breaking of Electroweak Symmetry Breaking (m W vs m Z ); (m W vs m Z );  Predict heavy particle masses and new physics scale (m top, m H,  ?) new physics scale (m top, m H,  ?) First Lecture Outline: 1. Brief History & Overview 2. Brief Theory Reminder: Why is Precision needed? Why is Precision needed? 3. List of “Electroweak” Observables 4. A few Precision Measurements Z Lineshape & Beam Energy (LEP)Z Lineshape & Beam Energy (LEP) Left-Right AsymmetryLeft-Right Asymmetry and Beam Polarization (SLC) and Beam Polarization (SLC) Heavy Flavour Rates (LEP&SLC)Heavy Flavour Rates (LEP&SLC) W mass (LEP)W mass (LEP) 5. The top mass prediction 6. The Higgs boson mass prediction 7. Standard Model consistency

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 3 A Little Bit of History 1967: Electroweak unification, with W, Z and H (Glashow, Weinberg, Salam); and H (Glashow, Weinberg, Salam); 1973: Discovery of neutral currents in  e scattering (Gargamelle, CERN)  e scattering (Gargamelle, CERN) 1974: Complete formulation of the standard model with SU(2) W  U(1) Y (Illiopoulos) model with SU(2) W  U(1) Y (Illiopoulos) 1981: The CERN SpS becomes a pp collider; LEP and SLC approved before W/Z LEP and SLC approved before W/Z discovery; discovery; 1983: W and Z discovery (UA1, UA2); LEP and SLC construction start; LEP and SLC construction start; UA2 First Z detected in the world: 1989: First collisions in LEP and SLC; Precision tests of the SM (m top ); Precision tests of the SM (m top ); 1995: Discovery of the top (FNAL); Precision tests of the SM (m H ); Precision tests of the SM (m H ); 2000: First hints of the Higgs boson? - qq  Z  e + e - -

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 4 ak Symmetry Breaking LEP Overview: Luminosity, Energy, Precision Z W H Total Luminosity: 1000 pb Precision: 0.1% LEP 1 LEP1.5 LEP 2 Energy: 88  GeV Conventional collider e + e - ring; Conventional collider e + e - ring; Energy upgradeable; Energy upgradeable; Energy measurable; Energy measurable; Four detectors (A,L,D,O); Four detectors (A,L,D,O); Large luminosity; Large luminosity; 20 Million Z events. 20 Million Z events. 4

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 5 Stanford Linear Collider Overview First high energy e + e - “linear” First high energy e + e - “linear” collider (with arcs); collider (with arcs); Reduced luminosity; Reduced luminosity; 73% polarized electron beam; 73% polarized electron beam; Small transverse beam sizes; Small transverse beam sizes; Small beam pipe; Small beam pipe; Only one detector (MarkII, SLD) Only one detector (MarkII, SLD) 350,000 Z events 350,000 Z events SLD Run COMPLEMENTARY to LEP

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 6 Why is Precision Needed? with L Couplings (v+a)  R Couplings (v-a) Electroweak Observables (i.e., related to W and Z) sensitive to vacuum polarization effects: 0.1% Precision needed! Determine  and sin 2  W from LEP/SLD data; Determine  and sin 2  W from LEP/SLD data; Predict m top and m W ; Predict m top and m W ; Compare with direct measurements; Compare with direct measurements; Predict m H; Predict m H; Compare with direct measurements. Compare with direct measurements. eff

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 7 Quantum Corrections to  (m Z ) (I) … e, ,  u,d,c,s,btop Common quantum (energy-dependent) corrections to  and Z can be absorbed in a redefinition of the QED coupling constant  (also called “running”) Precise QED Calculation Small,  log m top Calculate Evaluatefrom: e + e -  hadrons at various  s + QCD predictions

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 8 Quantum Corrections to  (m Z ) (II) Results more and more precise:  More e + e - data at low energy (in particular with BES) (in particular with BES)  Better knowledge of QCD at low energy (proven by hadronic low energy (proven by hadronic  decays studied at LEP)  decays studied at LEP)   had (m Z ) =    (m Z ) = 1/ (27) (most precise, most up-to-date) (5) Will improve soon with BaBar

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 9 Precision Electroweak Observables (I) Heavy Flavour Rates LEP1LEP1 LEP2LEP2

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 10 Dependence on m top, m H of m W and R b 0.5% Precision needed (m W /m Z ) 2  (m W /m Z ) 2  (1+  r) (No m H !) R b  R b (1+  Vb ) (Different m top, m H dependence) 1. W mass: Specific Vacuum Polarization 2. Z  bb decay rate: Specific Vertex Correction -

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 11 Precision Electroweak Observables (II) LEPLEPLEPLEP High Luminosity Precise Energy Precision of the Detectors + b-Tagging  -selection... sin 2  W to Consistency Checks! 1-4|Q i |sin 2  W Polarized Beam (SLC only)   Z     e.g. mWmW eff eff eff sin 2  W = 1 – m W 2 /m Z 2 (1+  )

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 12 The Z Lineshape at LEP At tree-level:  s = 1)Measure  and s 2)Correct for QED and QCD -30% for  MeV for m Z +4% for  qq 3)Fit for the Z parameters (mass, total width, peak cross (mass, total width, peak cross section and partial widths) section and partial widths)  (1+  )

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 13 Process very sensitive to imperfections Process very sensitive to imperfections (  slow, typically hours, and limited (  slow, typically hours, and limited to o(10%) polarization) to o(10%) polarization) Process very sensitive to beam-beam Process very sensitive to beam-beam interactions (  one beam, no polarization interactions (  one beam, no polarization in collisions) in collisions) Measurement of the LEP Beam Energy (I) LEP (L = 2  R = 27km) R B dipole e-e-e-e- p  Approximation: LEP is a circular ring immersed in a uniform magnetic field: E  p = e B R = (e/2  ) B L In real life: B non-uniform, ring not circular To be measured 1) The electrons get transversally polarized (i.e., their spin tends to align with B), but (i.e., their spin tends to align with B), but

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 14 Measurement of the LEP Beam Energy (II) BxBxBxBx -B x 2) The spin precesses around B with a frequency proportional to B. a frequency proportional to B. The number of revolutions The number of revolutions for each LEP turn is thus for each LEP turn is thus proportional to B L (in fact, proportional to B L (in fact, to  B dl, and then to E beam ) to  B dl, and then to E beam ) B Peak Peak Peak+2 3) Measure s : B x : oscillating field with frequency, in one point. Vary until Polarization = 0 Precision  2   E beam  100 keV ! 1993

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 15 Measurement of the LEP Beam Energy (III)  S S U U N N S S U U N N A dispersion of 10 MeV is observed (  100 keV) in the same machine conditions. Correlation with the moon found on 1992, Nov 11 th : LEP at noon Shorter by 300  m LEP at midnight Longer by 300  m However, the electron orbit length is fixed by the RF frequency: L = c   t At midnight, the electrons see At midnight, the electrons see less magnetic field, E is smaller; less magnetic field, E is smaller; At noon, they see more magnetic At noon, they see more magnetic field, and E is larger. field, and E is larger. Prediction and data fit perfectly …

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 16 Measurement of the LEP Beam Energy (IV) B dipole RF frequency: Hz (  1 Hz) Electron orbit fixed by RF

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 17     QUAD QUAD QUAD QUAD Beam Orbit Monitors (BOM) Dipole Dipole

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 18 Other 10 MeV-ish effects understood even later:  Effect of the rain: water pressure in the mountains change LEP circumference; mountains change LEP circumference; (controlled with the BOM’s) (controlled with the BOM’s)  Effect of the TGV: currents induced on the LEP beam pipe change the magnetic field LEP beam pipe change the magnetic field (controlled by 16 NMR probes) (controlled by 16 NMR probes) Measurement of the LEP Beam Energy (V) Understood after three rainy months Understood after one-day strike Now:  E beam  2 MeV

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 19 Z Lineshape: Final State Identification (I)

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 20 Z Lineshape: Final State Identification (II) e) Z-> - Z  qq : Two jets, large particle multiplicity. Z  qq : Two jets, large particle multiplicity. Z  e + e -,  +  - : Two charged particles (e or .) Z  e + e -,  +  - : Two charged particles (e or .) Z   : Z   : Not detectable. - - Z   +  - : Two low multiplicity jets + missing Z   +  - : Two low multiplicity jets + missing energy carried by the decay neutrinos energy carried by the decay neutrinos

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 21 Z Lineshape: Final State Identification (III) Systematic Uncertainty  0.1% Hadronic decays: High multiplicity High mass Leptonic decays: Low multiplicity, with (  ) or without (e,  ) missing energy Selections with  High Efficiency;  High Purity; Count events : Easy? 16 million 600, ,000  Collisions: Low multiplicity, Low mass

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 22 Z Lineshape: Results (I) MEASURE MEASURE Dominant (and common) error: LEP Beam Energy Measurement  s varied from 88 to 94 GeV;  s varied from 88 to 94 GeV; Points are from data in both Points are from data in both coordinates; coordinates; Lines are from a standard model Lines are from a standard model fit to the Z parameters; fit to the Z parameters; 10 -5

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 23 Z Lineshape: Results (II) N  =  DELPHI L3 OPAL N = 2 N = 3 N = 4 13 October 1989 L3: 2538 hadronic Z’s ALEPH: 3112 hadronic Z’s OPAL: 4350 hadronic Z’s DELPHI: 1066 Hadronic Z’s L3 ALEPH DELPHI OPAL 13-Oct-1989: N = 3.16  0.20 N = 3.42  0.48 N = 3.27  0.30 N = 3.1  0.4 N = 2.4  0.4 Three Weeks after start MarkII, Aug. 1989, with 106 Z decays: N  = 3.8  1.4.

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 24 Z Lineshape: Results (III)  had /  l MeV in 1989 (1998)  Z  (1 +  ) With this measurement alone: m top  165  25 GeV/c 2 (+small sensitivity to m H ) 10 -3

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 25 Heavy Flavour Rates: Identification (I) b- and c-hadrons decay weakly towards c- and s-hadrons, with a macroscopic lifetime (1.6 ps for b’s), corresponding to few mm’s at LEP  10 cm  1 cm 3d-vertexing determines secondary and tertiary vertices. High resolution is crucial. Impact parameters of reconstructed tracks allow b quarks to be tagged with very good purity. Mass of secondary vertex tracks is a very powerful discriminator of flavour (b, c, and light quarks): m b  5 GeV/c 2, and m c  1.5 GeV/c 2.

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 26 Heavy Flavour Rates: Identification (II) Vertex Mass for Events With a Secondary Vertex In SLD Vertex Mass (GeV/c 2 ) b (MC) c (MC) uds (MC) Data Vertex detectors (Si  -strips, CCD’s, pixels): At LEP: inner radius 6 cm, good resolution; At LEP: inner radius 6 cm, good resolution; At SLC: inner radius 2.3 cm, superior resolution. At SLC: inner radius 2.3 cm, superior resolution. SLD can do both b- and c-tagging with good purity.

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 27 Heavy Flavour Rates: Results Use double-tag method to reduce uncertainties from the simulation, e.g., in bb events: Take  c,  uds, and  b (all small) from simulation. Solve for  b and R b ! With this measurement alone: m top  150  25 GeV/c 2 (dependence on m H,  s, … cancel in the ratio) R b =  bb /  had -

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 28 Prediction of m top from EW Measurements (actually 2.9  ) A top mass of 177 GeV/c 2 was predicted by LEP & SLC with a precision of 10 GeV/c 2 in March One month later, FNAL announced the first 3  evidence of the top. In 2001: Perfect consistency between prediction and direct measurement. Allows a global fit of the SM (with m H ) to be performed. / SLD

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 29 Asymmetries: Measurement of A LR at SLD (I)  A LR (  A e ~ 14% if P e = 100%) is 10 times more sensitive to sin 2  W than A FB (  A e A l ~ 1-2%); than A FB (  A e A l ~ 1-2%);  A LR is independent of the final state (Z  hadrons,  +  -,  +  - );  A LR is independent of the detector acceptance;  Most of the theoretical corrections, uncertainties (QED, QCD, …) cancel in the A LR ratio. cancel in the A LR ratio. Statistical&Systematic uncertainties compete with LEP asymmetry measurements (e - beam polarization) (unpolarized) lept

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 30 Asymmetries: Measurement of A LR at SLD (II) Condition # 1: Have a longitudinally  100% polarized electron beam.  Get longitudinally polarized e - by illuminating a GaAs photo cathode with circularly polarized Lasers (frequency: 2  60 = 120 Hz) circularly polarized Lasers (frequency: 2  60 = 120 Hz)  In principle, P e  100% can be reached. In practice, 80% was achieved.  Change the sign of the polarization on a random basis to ensure that on a random basis to ensure that equal amount of data are taken with equal amount of data are taken with both signs, and that the luminosity both signs, and that the luminosity is not tied to any periodic effects is not tied to any periodic effects in SLC. in SLC.  Transport, accelerate and collide the polarized electrons, with enough care polarized electrons, with enough care to keep the same polarization at the to keep the same polarization at the interaction point. SLC was designed interaction point. SLC was designed to do so from the beginning (unlike to do so from the beginning (unlike LEP). LEP).

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 31 Asymmetries: Measurement of A LR at SLD (III) Condition # 2: Measure the e - polarization P e with 0.5% accuracy.  Collide 45.6 GeV long. polarized e - with 2.33 eV (532 nm) circularly polarized 2.33 eV (532 nm) circularly polarized photons every 7 th bunch (17 Hz); photons every 7 th bunch (17 Hz);  Detect Compton back-scattered e - as a function of their energy after a bend a function of their energy after a bend magnet; magnet;   (E) =  0  [1 + A(E) P e P  ] 0000 A(E) Cerenkov Detectors  0 and A(E) are theoretically well known (pure QED process)

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 32 Asymmetries: Measurement of A LR at SLD (IV)  Reverse on a random basis the sign of the photon polarization P  (close to 100%, optically measured with filters); (close to 100%, optically measured with filters);  Count the number of e - detected in each of the Cerenkov channels (about a hundred electrons per channel at each beam crossing) (about a hundred electrons per channel at each beam crossing)  Deduce the e - beam polarization from the asymmetry Uncertainty  P/P Laser Polarization0.1% Analyzing Power0.4% Linearity0.2% Electronic Noise0.2% TOTAL0.5%

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 33 Asymmetries: Measurement of A LR at SLD (V) Cross-checks:  Count Compton-scattered gammas at the kin. threshold with two additional calorimeters. threshold with two additional calorimeters. Agree with the main measurement to 0.4%. Agree with the main measurement to 0.4%.  Measure the positron polarization to be 0.0% with an accuracy better than 0.1%. with an accuracy better than 0.1%. Condition # 3: Count events in SLD e.g., in : o N L = 183,355; N R = 148,259 o P e = 72.92%  A e =  (stat.)  (syst.)  A e =  (stat.)  (syst.) Complete data set:

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 34 Asymmetries: Results for sin 2  W Leptons:  Quarks:  ??? Still statistically acceptable, but a couple of add’l years at LEP and SLD would have helped… eff ALL: 

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 35 Asymmetries: Results for a l and v l Errors  10  200 Before LEP&SLC After LEP&SLC Axial and vector couplings (a l, v l ) from A LR (SLC) and Z  l + l - (LEP) Precision on sin 2  W : , adequate to become sensitive to m H.

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 36 Asymmetries: Prediction of m W Predict m W in the SM: m W 2 = m Z 2 (1+  )cos 2 W eff Direct Measurements* Precision Measurements m H dependence in the SM through quantum corrections (see later) * Coming now for m W at LEP; See Y.-K. Kim lecture for m top See Y.-K. Kim lecture for m top and m W at the Tevatron. and m W at the Tevatron.

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 37 W + W -  q 1 q 2 l : Two hadronic jets, Two hadronic jets, One lepton, missing energy. One lepton, missing energy. W mass at LEP 2: Production and Decay W + W -  q 1 q 2 q 3 q 4 : Four well separated jets. Four well separated jets W + W -  l 1 1 l 2 2 : Two leptons, missing energy Two leptons, missing energy  s  2m W 45.6% 43.8% 10.8%

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 38 W mass at LEP 2: Threshold cross section m W (thresh.) = (80.40  0.22) GeV/c 2

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 39 W mass at LEP 2: Direct measurement (I) 5 Constraints: 0 unknowns, 5C fit 3 unknowns, 2C fit Fitted mass (GeV) Initial State Radiation; Initial State Radiation; (change the effective beam energy) (change the effective beam energy) Detector Resolution; Detector Resolution; (change the jet directions) (change the jet directions) Other four-fermion diagrams Other four-fermion diagrams (create non-Breit-Wigner bkgds) (create non-Breit-Wigner bkgds)

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 40 W mass at LEP 2: Direct measurement (II)  Mostly rely on simulated mass distributions to determine m W m W (qqqq) =  GeV/c 2 m W (qql ) =  GeV/c 2 LEP Combination: Good compatibility between the two final state:  m = 9  46 MeV/c 2 10,000 W pairs per experiment

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 41 W mass at LEP 2: Result and Uncertainties Good consistency between experiments; Good consistency between experiments; Good consistency with hadron colliders Good consistency with hadron colliders (see Y.-K. Kim lecture); (see Y.-K. Kim lecture); Good consistency with Z data (LEP/SLD). Good consistency with Z data (LEP/SLD). m W (LEP) =   (stat.) (syst.) (stat.) (syst.) Limited by systematic uncertainties on final state interaction (Bose-Einstein Correlation and Colour Reconnection).

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 42 W mass at LEP 2: Final State Interactions + = Interactions between W hadronic decay products may cause a shift between the mass from fully hadronic and semileptonic events: Colour Reconnection: QCD interaction between Colour Reconnection: QCD interaction between quarks from different W’s; quarks from different W’s; Bose-Einstein Correlations between identical Bose-Einstein Correlations between identical hadrons (pions, kaons), well established in single hadrons (pions, kaons), well established in single W or Z decays. W or Z decays. Use the data to constrain them ! q q q q Without FSI SMALL SMALL

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 43 Global Fit of the Standard Model to m H (I) Knowing m top, most electroweak observables have a sensitivity to m H through 

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 44 Global Fit of the Standard Model to m H (II) Global fit of m H and m top :

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 45 Global Fit of the Standard Model to m H (III) Mean: 0.22  0.28 Sigma: 1.1  0.4 Internal Consistency of the Standard Model? Largest discrepancy (-2.9  ) well inside statistical expectation;  2 probability = 8%. Just fine. Pull distribution = Normal Gaussian?

SLAC Summer Institute August 13-24, 2001 Probes of Electroweak Symmetry Breaking at LEP and SLC 46 Global Fit of the Standard Model to m H (IV) What Next? 1 st Lecture Conclusions  Now:  m top =  5.1 GeV,  m W =  34 MeV  With  m top =  2 GeV  With  m W =  15 MeV  With  m top =  2 GeV and  m W =  15 MeV  LEP and SLD allowed the internal consistency of the standard model consistency of the standard model to be tested with great precision; to be tested with great precision;  LEP and SLD checked the predictions of the Electroweak Symmetry Breaking of the Electroweak Symmetry Breaking mechanism (e.g., m W = m Z  cos  W ); mechanism (e.g., m W = m Z  cos  W );  LEP and SLD allowed the mass of the top quark to be predicted several years top quark to be predicted several years before it was discovered in 1995 at the before it was discovered in 1995 at the Fermi National Laboratory; Fermi National Laboratory;  LEP and SLD measurements led to the prediction of a relatively small Higgs prediction of a relatively small Higgs boson mass (around 100 GeV/c 2 ); boson mass (around 100 GeV/c 2 );  Future Machines (Tevatron, LHC, LC) will be important for EW Physics. will be important for EW Physics.