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Precision Tests of the Electroweak Interactions

This paper discusses the parameters of the Standard Model and various tests of the electroweak interactions at low and high Q^2. It also explores the consistency of these tests with the predictions of the Standard Model and constraints on the Higgs boson mass. The future prospects in this field are also presented.

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Precision Tests of the Electroweak Interactions

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  1. Precision Tests of the Electroweak Interactions Frederic Teubert CERN, PH Department ICHEP04 - Frederic Teubert

  2. Outline • Introduction Parameters of the SM. • Test of the EW interactions at low Q2 g-2 and the running of (Q2) sin2eff measurements • Test of the EW interactions at high Q2 Z mass/width and couplings W mass/width and couplings Top quark mass • Consistency with the SM predictions Consistency with the SM Constraints on mHiggs. • Future prospects • Outlook many thanks to many people, in particular: D.Alton, H.Burkhardt, M.Carena, R.Chierici, P.Cushman, J.G.DaCosta, M.Davier, C.DeClercq, A.Gurtu, M.Gruenewald, E.Halkiadiakis, C.Hays, R.Hawkings, A.Hoecker, P.Langacker, K. Nagano, L.Malgeri, B.Q.Ma, B.McKeown, M.Muehlleitner, R.Petti, B.Pietrzyk, G.Quast, B.Quayle, R.Ranieri, P.Renton, H.Ruiz, E.Sauvan, J.Stirling, J.Shan, A.Tapper, E.Torrence, G.Venanzoni, S.Yost, B.Zhang ICHEP04 - Frederic Teubert

  3. Parameters of the SM Parameters of the Standard Model. In the context of the SM, any EW process can be computed at tree level from , mW , mZ. When higher orders are included, any observable can be predicted as Contrary to what happens with “exact gauge symmetry” theories, like QED or QCD, the effect of heavy particles do not decouple, and there is sensitivity to mtop and to less extend to mHiggs, or to any kind of “heavy new physics”. O(, mW, mZ, s, mHiggs, mtop) and the rest of mf which are known with adequate precision On-Shell renormalization scheme ICHEP04 - Frederic Teubert

  4. Parameters of the SM The usual procedure has been to take G, the Fermi Constant measured in muon decay, to predict mW and use this more precise value to predict any other observable. Therefore, the input parameters are chosen to be: But… the relevant scale is q2  m2Z … -1(0) = 137.03599877(40) s(mZ) = 0.118(2) G (m)=1.16637(1) 10-5GeV-2 mZ = 91.1875(21) GeV 310-9 210-2 910-6 210-5 ICHEP04 - Frederic Teubert

  5. Parameters of the SM: (Q2)   The running of (Q2). Since vacuum polarization effects screen the electric charge, the coupling increases when evaluated at a high scale of the  momentum transfer… The shift  can be determined analytically for lepton loops and by a dispersion integral over the e+e- annihilation cross section for light quarks (u,d,s,c,b): (m2Z) = /(1-) a ~ (Q2)/2 Optical Theorem ICHEP04 - Frederic Teubert

  6. Parameters of the SM: (Mz2) Using the latest experimental data from BESII: 5hadron = 0.02761 0.00036 (Burkhardt and Pietrzyk 2001) 5hadron = 0.02755  0.00023 (Hagiwara et al. 2003) These data has also confirm the validity of extending the use of perturbative QCD in the calculation of 5hadron. The most precise of these theory-driven calculations gives, 5hadron = 0.02747  0.00012 (Troconiz and Yndurain 2001) using CMD-2 and KLOE latest data, seem to cancel out using CMD-2 latest data  is not anymore the limiting factor in the SM fits… thanks BES !!! hep-ph/0312250 ICHEP04 - Frederic Teubert

  7. Parameters of the SM: (~M2) e+ τ- e- ν γ W π+ π0 π- π- (11658472.07± 0.11)10-10 (692.4 to 694.4 ± 7)10-10 [e+e- -based 04] (12.0 ± 3.5)10-10 [Melnikov & Vainshtein 03] ICHEP04 - Frederic Teubert

  8. Comparison KLOE vs CMD-2 ampp = (375.6  0.8stat  4.8syst+theo)  10-10 KLOE 1.3% Error ampp = (378.6  2.7stat  2.3syst+theo)  10-10 CMD-2 0.9% Error |Fp | 2 CMD-2 KLOE only statistical errors are shown KLOE PRELIMINARY comparison with CMD-2 in the range 0.37 GeV2 < Mpp2 < 0.93 GeV2 Mpp2 (GeV2)  evaluated using e+ e- data preferred, however more data needed: BaBar, Belle,KLOE … ICHEP04 - Frederic Teubert

  9. Radiative Corrections Quantum loops generate corrections in three sectors: DEFINITION  = 0 / (1-) a =  I3 v =  I3 (1 - 4|Q|  sin2W) sin2W  1 - m2W/m2Z (1+r) r   + rW (mTop, mHiggs)  0.06 - 0.014   (mTop, mHiggs)  0.005 sin2eff •  1 + QED + w (mTop, mHiggs)  1 + 0.038 + 0.002 ICHEP04 - Frederic Teubert

  10. Tests of the EW interactions at low Q2 ICHEP04 - Frederic Teubert

  11. (g-2) a B When=29.3(p=3.09 Gev/c), ais independent of E. B is determined by measuring the proton nuclear magnetic resonance (NMR) frequency p in the magnetic field. N(t)=Ne-t/[1-Acos(ωat+φ)] ICHEP04 - Frederic Teubert

  12. (g-2) BNL01 m- (0.7 ppm) BNL00 m+ (0.7 ppm) New -data collected in 2001, confirms previous measurements using + (a+ - 11659000)x 10-10 = 203 ± (6 stat.  5 syst.) (a- - 11659000) x 10-10 = 214 ± (6 stat.  5 syst.) (a - 11659000)exp x 10-10 = 208 ± (5 stat.  4 syst.) (a - 11659000)th x 10-10 = 183 ± 7[e+e-] DEHZ04 including KLOE 2.7 from prediction (was 1.9 before inclusion of 2001 data) ICHEP04 - Frederic Teubert

  13. sin2eff at low Q2 (E-158) sin2eff(Q2=0.026 GeV2) =0.2403±0.0010 (stat)±0.0009 (syst) (Run I + II + III, preliminary) Møller scattering : Scatter polarized (up to 80%) 50 GeV electrons off unpolarized atomic electrons, and measure the asymmetry However, (Q2) completely dominated by (Q2), hence mostly sensitive to new physics at born level (eg. Z’, LFV, Contact Interactions, …) ICHEP04 - Frederic Teubert

  14. sin2eff at low Q2 (NuTeV) Uncertainties from modelling such as charm mass and strange sea… alternatively, measure CC and NC in both neutrinos and anti-neutrinos: Paschos-Wolfenstein method Large cancellation of uncertainties ! R= 0.3916 ± (0.0007 stat.  0.0011 syst.) SM: 0.3950 (-2.6 ) R= 0.4050 ± (0.0016 stat.  0.0022 syst.) SM: 0.4066 (-0.6 ) ICHEP04 - Frederic Teubert

  15. sin2eff at low Q2 (NuTeV) The Strange Sea: The computation assumes that the strange sea is symmetric. New CTEQ analysis including the NuTeV dimuon data gives, while to explain the whole effect would require +0.006 Possible sources of discrepancy Electroweak corrections: New calculations: K.Diener et al. hep-ph/0310364, hep-ph/0311122 Kretzer, hep-ph/0405221, Arbuzov et al., hep-ph/0407203 Improved treatment of initial state mass singularities Could reduce the discrepancy by about 1 Isospin Violation: Could up(x)  dn(x) ? Can account for about 1 of the effect. Before a careful re-assessment of all theoretical uncertainties, the 3 discrepancy with the SM cannot be taken at face value. ICHEP04 - Frederic Teubert

  16. sin2eff at low Q2 (NOMAD) ICHEP04 - Frederic Teubert

  17. Lepton Flavor Violationat BaBar/BELLE 220 Million +- ICHEP04 - Frederic Teubert

  18. Tests of the EW interactions at high Q2 ICHEP04 - Frederic Teubert

  19. p p Z/W production e,m e+, m+ q q Z0/g* W± n e-, m- Van Neerven, Matsuura q p q’ p Van Neerven, Matsuura Total Luminosity: 1000 pb-1 Run II Luminosity: 400 pb-1 since 2001 TeVatron Run II 200k leptonic Z’s 20 Million Z’s Precision: 0.1% 40,000 W+W- Energy: 1800 2000 GeV 1989-2000 LEP Run 2 Million leptonic W’s Energy: 88 209 GeV A few Higgses? ICHEP04 - Frederic Teubert

  20. Polarized cross-sections at HERA II HERA II Luminosity: ~20 pb-1 HERA II e+ polarization: 32% and -40% Q2 > 400 GeV2 Y < 0.9 CC (P=-1)= -3.7  2.4  2.7 pbH1 ICHEP04 - Frederic Teubert

  21. Multi-lepton events at HERA ICHEP04 - Frederic Teubert

  22. Gauge Bosons at TeVatron CDF/D: • Measurement of many cross-sections • Limits on couplings in progress CDF/D Compare to Drell-Yan • Set limits on Z’, extra dimensions, etc. • Improve on Run I limits, test new models 95% CL, M(Z’/SM) > 735 GeV ICHEP04 - Frederic Teubert

  23. Z lineshape at LEP Final results from LEP: mZ = 91.1875 0.0021 GeV Z = 2.49520.0023 GeV 0h =41.540 0.037 nb Rl = 20.767 0.025 (5.4 )  = 0.0054  0.0010 • The invisible width defined as inv  Z - h - (3+) l = 499.0  1.5 MeV • allows to quote a limit on invisible non SM Z decays as: • Number of light neutrino species: N  inv /l  (l /)SM • (-1.9) inv < 2.1 MeV @ 95% c.l. N = 2.9841  0.0083 0.0054 (theor.)  0.0063 (exp.) ICHEP04 - Frederic Teubert

  24. Z couplings to leptons The measurements of Asymmetries at the Z pole are determinations of the ratio: Average of LEP: AlFB , APOL SLC: ALR(2/dof = 1.6/2) Al = 0.1501  0.0016 and using the leptonic width, sin2eff = 1/4 (1-glV/glA) =  sin2W sin2eff = 0.23113  0.00021 ICHEP04 - Frederic Teubert

  25. Z couplings to quarks AFB The measurements of Asymmetries away from the Z pole measure the interference between  and the Z. ICHEP04 - Frederic Teubert

  26. Z couplings to quarks Flavour tagging allows precise measurements of the heavy quarks partial widths and asymmetries, Rc  c/q ,Rb  b/q , AcFB,AbFB Lifetime tagging: • Most efficient way of selecting b-hadrons from Z decays, Average b lifetime (1.5 ps) average path 3 mm. • Impact Parameter of b-decay products is about 300 m. • Mass information is used to discriminate between b-hadrons and c-hadrons (mb >> mc) With the lifetimetagging high purity b samples are selected (~95%) while keeping good efficiency(~30%). Impact parameter Invariant mass ICHEP04 - Frederic Teubert

  27. Z couplings to quarks New combination from LEP and SLC, 2 = 53.0 / (105-14) New theoretical uncertainty in the Z interference added : 0.0005 AFB = 0.0998 ± 0.0017 (summer 04) AFB = 0.0997 ± 0.0016 (summer 03) ICHEP04 - Frederic Teubert

  28. Z couplings to leptons/quarks sin2eff comparison : which corresponds to a 2.8 disagreement. 2.8 (it was 2.9)between the two most precise quantities (ALR vs AbFB) sin2eff = 0.23213  0.00029 (q-asym.) sin2eff = 0.23113  0.00021 (l-asym.) sin2eff = 1/4 (1-glV/glA) ICHEP04 - Frederic Teubert

  29. W decays Tree level NNLO QCD calc (Van Neerven) SM EWK Calculation PDG(LEP) RUN II Preliminary CDF combined electron & muon channels LEP II A/D/L Final, O Preliminary combined electron & muon channels BR(Wl) = (10.63 0.12) % while from the tau channel (3) BR(W) = (11.41  0.22) % ICHEP04 - Frederic Teubert

  30. Triple Gauge Boson Couplings AD prel. LO final g1Z = -0.009  0.022  = -0.016  0.044  = -0.016  0.022 Consistent with the SM with a precision of O(2-4%). ICHEP04 - Frederic Teubert

  31. W mass at TeVatron Example of what can be achieved with Run II at CDF, using W  decays: mW ( , RUN I)= 80.465  0.100  0.103 GeV mW ( , 200 pb-1 RUN II)= 80.xxx  0.050  0.069 GeV Final RUN I results mW (RUN I)= 80.454  0.033  0.050 GeV ICHEP04 - Frederic Teubert

  32. W mass at LEP q W- e- _ q d~0.1 fm e+ W+ q _ q Expected final statistical error for LEP: ~ 25 MeV • Interconnection effects (not included in standard MC models): • Bose-Einstein correlations: momenta of identical bosons tend to be correlated. • Colour reconnection: hadronic interaction between W decays • d(W+,W-) < 1 fm ICHEP04 - Frederic Teubert

  33. W mass at LEP:( exp. limits on BE/CR) CR: L3 A W- C W+ D B mW (BE)= ~15 MeV mW (CR)= ~100 MeV mW (4q) - mW (2q) = 22 ± 43 MeV ICHEP04 - Frederic Teubert

  34. W mass at LEP: (Color Reconnection) • Proposed solution: modify clustering algorithm to dismiss information from those particles. K parameter • Good reduction factors are obtained for all available models • Example: Cone (R=0.5 rad), with a statistical loss of ~ 25%: ICHEP04 - Frederic Teubert

  35. W mass mW (world average)= 80.425  0.034 GeV • Good consistency between LEP experiments • Good consistency LEP/TeVatron experiments • Consistency with Z data (LEP/SLD): • mW=mZ cosW world average leptons quarks mW= 80.414  0.026 GeV(cosW from leptons) mW= 80.290  0.042 GeV(cosW from quarks) mW (LEP)= 80.412  0.029  0.031 GeV ICHEP04 - Frederic Teubert

  36. Top mass at TeVatron The previous value of the top mass was: July 2000, Run I: mtop (CDF)= 176.1  4.2  5.1 GeV mtop (D) = 172.1  5.2  4.9 GeV D has re-analized the Run I data with a much more detailed event-by-event likelihood: April 2004, Run I: mtop (D) = 180.1  3.6  3.9 GeV April 2004, Run I: mtop (CDF+D)= 178.0  2.7  3.3 GeV ICHEP04 - Frederic Teubert

  37. Consistency with the SM predictions ICHEP04 - Frederic Teubert

  38. Consistency with the SM Are we sensitive to radiative corrections other than ?: Rb: SM prediction with b = 0 Measurement (LEP+SLC) sin2eff: SM prediction with W = 0 Measurement (LEP+SLC) l: SM prediction with  = 0 Measurement (LEP) mW: SM prediction with rW = 0 Measurement (LEP+TEVATRON) (2.8 ) b = -0.0045  0.0016 mtop = 155  20 GeV Rb = 0.2183 Rb = 0.21646  0.00065 (1.7 ) sin2eff = 0.23115 sin2eff = 0.23147  0.00017 W = 0.0014  0.0008 (4.7 ) glA = -0.5 glA = -0.50123  0.00026  = 0.005  0.001 (12 ) rW = -0.023  0.002 mW = 80.026 mW = 80.425  0.034 ICHEP04 - Frederic Teubert

  39. Consistency with the SM mtop = 174±5.1 GeV178.0  4.3 GeV sin2eff (b-asym) = 0.23212±0.000290.23210  0.00030 All the high Q2 measurements are fitted as a function of: O( , G , mZ , s , mHiggs ,mtop) • Changes w.r.t. summer 03: • New measurement of mtop at TeVatron: • New HF average from LEP: • New version of ZFITTER v6.4 with two loop corrections to Mw and sin2eff ICHEP04 - Frederic Teubert

  40. Consistency with the SM mtop (fit) = 179 ± 10 GeV (2/dof = 15.8/12) mtop (exp) = 178.0 ± 4.3 GeV mW (fit) = 80.379 ± 0.023 GeV (2/dof = 14.1/11) mW (exp) = 80.425 ± 0.034 GeV ICHEP04 - Frederic Teubert

  41. Consistency with the SM SM fits: with a 2/d.o.f. = 15.8/13 and a 67% correlation between mtop and log(mHiggs). The largest contribution to the 2 is AbFBwith 2.4. It pulls for a large mHiggs in opposition to l, mW and leptonic asymmetries. 5hadron = 0.02769 0.00035 s(mZ) = 0.1186  0.0027 mtop = 178.2  3.9 GeV log(mHiggs) = 2.06  0.21 ICHEP04 - Frederic Teubert

  42. Constraints on mHiggs log(mHiggs) = 2.06  0.21 mHiggs = 114 + 69- 45 GeV mHiggs < 260 GeV @95% c.l. mHiggs > 114 GeV @95% c.l. ICHEP04 - Frederic Teubert

  43. Constraints on mHiggs Is there any chance to improve this constraints? [log(mHiggs)]2 = [exp]2 + [mt]2 + []2 + [s]2 Z asymmetries,sin2eff :[0.22]2 = [0.15]2 +[0.12]2+ [0.10]2 + [0.01]2 all high Q2 data:[0.21]2 = [0.12]2 +[0.13]2 + [0.10]2 + [0.04]2 [0.03] if theory-driven The reduction in mtop (5.1  4.3 GeV) has reduced the uncertainty on mHiggs , but still the TOP priority is to reduce the uncertainty on mtop ,which is limited by systematic uncertainties! ICHEP04 - Frederic Teubert

  44. Future prospects ICHEP04 - Frederic Teubert

  45. Future prospects What do we learn from all this impressive experimental effort is that something has to happen at energy scales ofO(1 TeV). It may be a light Higgs boson, it may be SUSY, or it may even be something else… but the scale is fixed by the precision EW measurements at LEP/SLC/TeVatron. ICHEP04 - Frederic Teubert

  46. Future prospects CMS NOTE 2003/033  theory-driven  log(mHiggs) 0.18 0.10 now 0.08 run II LHC 0.05 LC ICHEP04 - Frederic Teubert

  47. Future prospects What could be better than an e+e- linear collider to complement with precision, the measurements at the hadron colliders at the TeV scale? ICHEP04 - Frederic Teubert

  48. Outlook ICHEP04 - Frederic Teubert

  49. Outlook The standard model of ElectroWeak interactions describes all precision measurements, O(0.1%). The precision is such that one needs to add pure EW radiative corrections sensitive to heavy particles: Any improvement on this indirect determination of mHiggs needs an improvement on the uncertainty on mTop. The largest contribution to the 2 is AbFBwith 2.4. It pulls for a large mHiggsin opposition tol, mW and leptonic asymmetries. mtop = 178.2  3.9 GeV mHiggs = 114 + 69- 45 GeV (2/dof = 16/13) mHiggs < 260 GeV @95% c.l. ICHEP04 - Frederic Teubert

  50. Outlook The biggest discrepancy is on the interpretation of the ratio of NC and CC as measured by NuTeV as a determination of sin2eff. However this interpretation depends on theoretical uncertainties that must be reevaluated, before the 3 discrepancy is taken at face value. The biggest challenge to the SM is the deviation in the measurement of the anomalous magnetic moment of muons: which is 2.7 away from theory. The theoretical prediction is now much more robust, even though the discrepancy with tau data is not really understood. The medium-term future is bright in our field. The EW precision measurements tells us that something has to happen at energy scales of O(1 TeV)… which happen to be the energy scale of LHC and e+ e- linear colliders. (a - 11659000)exp x 10-10 = 208 ± 6 (a - 11659000)th x 10-10 = 183 ± 7 ICHEP04 - Frederic Teubert

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