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Electroweak Symmetry Breaking: experimental investigations

Electroweak Symmetry Breaking: experimental investigations. The question The tools : accelerators and detectors The status from precision electroweak measurements The status of direct searches The near future (Tevatron, LHC) The Susy factory: ILC The Higgs factory: muon collider

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Electroweak Symmetry Breaking: experimental investigations

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  1. Electroweak Symmetry Breaking: experimental investigations • The question • The tools : accelerators and detectors • The status from precision electroweak measurements • The status of direct searches • The near future (Tevatron, LHC) • The Susy factory: ILC • The Higgs factory: muon collider • Conclusions

  2. The Question: Why do W’s have mass (and photons dont)? The Standard Model answer: a complex doublet of self coupling scalars with weak isospin ½ splits off into W+L W-L W0L (additional degrees of freedom of massive particle) and h0 Furthermore, W0 and B field mix by angle qw to give Z and g mW+=mW-=mW0=mZcosqw mg = 0 This important test of the model (or is it?) is verified with high precision speed of em radiation is independent of wavelength residual energy carriedby vector potential (Arhonov-Boehm effect) Magneto hydrodynamics of solar plasma mg< 6 10 –17eV(new, PDG 2004) and of course is respected by em gauge invariance

  3. LEP ran around Z peak Z mass and width then up to 209 GeV collected 20MZ,& 80 kW

  4. Slac Linear Collider 92 GeV polarized e+e- collider ran at Z peak (500kZ) observed first Z event polarized beam (~77%) very small vertex  excellent b, c tag

  5. TeVatron 2 TeV proton-antiproton collider WZ event in D0 1000

  6. LHC These are real magnets now!

  7. PROGRAMME measure Z and W masses measure W check relation mW= mZcosW see that it is affected by Electroweak Radiative corrections use these to predict top quark mass find the top and check its mass use mass to refine Higgs boson mass from EWRCs try to find a physical h particle what if not? verify properties of W and Z, WW, WZ, ZZ scattering If yes, identify its properties, Susy or not – other Higgses ………

  8. EWRCs relations to the well measured GF mZ aQED at first order: Dr = a /p (mtop/mZ)2 - a /4p log (mh/mZ)2 e3 = cos2qwa /9p log (mh/mZ)2 dnb=20/13 a /p (mtop/mZ)2 complete formulae at 2d order including strong corrections are available in fitting codes e.g. ZFITTER

  9. 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

  10. 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]

  11. (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)

  12. luminosity measurement to 6 10-4! LEP: N = 2.9841 0.0083 Ginv (new)< 2.1 MeV NB this is 2s low

  13. energy resolution (resonant depolarization) +-200 keV! variations due to tides, trains, rain, etc.. mZ= 91187.5 +-2.1 MeV

  14. Note relative insensitivity of Gz to Higgs mass. Was the dominant new factor in 1994 when results from the 1993 scan (with res. dep. on each point)  GZ = 2494.8 +- 2.5 MeV mtop = 174 +- 12 +- 18 GeV Bolek Pietrzyk Moriond March 1994 vs mtop = 174 +- 16 GeV CDF may 1994 !

  15. Measuring sin2qWeff (mZ) sin2qWeff  ¼ (1- gV/gA) gV = gL + gR gA = gL - gR

  16. e+e-  mn qq W mass ALEPH evts e+e-  q1 q2 q3 q4 WZ event in D0

  17. NUTeV SM: combination of and yields mW and sin2qWeff(Q2) experiment expresses result in terms of   sin2qW  = 1 – m2W/m2Z which is strictly and obviously equivalent to mW once mZ is so well measured. beyond SM: sensitivity to unexpted Q2 dep. of couplings and or propagators (Z’) Trivial problems: predictions are sensitive to assumptions about isospin symmetry violations is u(x) in neutron strictly equal to d(x) in proton? charm production?

  18. Measuring masses with JETs • which may not be independent • LEP mW from the 4quark channel • W  qq gives two dependent jets • (in JETSET language these jets are part • of one single string) but they form a • COLOR SINGLET • WW qq qq gives two COLOR SINGLETS • which in principle shouldnt talk to each other • Is this true? It has been suspected that • there may be some O(as2) correction leading • for example to • Bose Einstein correlations between (BEB) • the two systems • Color reconnection effects • there has been some progress in trying to • see such effects in data. • This can affect WW 4q mass by > 100 MeV

  19. four quark channel is severely affeced by hadronization uncertainties!

  20. BEC in W+W- events LEPWW/FSI/2002-02 L3 fraction of model seen BEC effects experimentally established in Z jets at LEP1 Inter-W BEC? Analyses performed in 4 LEP experiments to search/limit them Observable: distance in p-space between pairs of charged pions: Q2ij=-(pi-pj)2 0 1 Q(GeV) • Inter-W BEC correlations disfavoured • Limit on systematic: dMW ~ 15 MeV

  21. The particle flow analysis • Data • - SK1 (extreme parameter) No CR: CR: A - Jetset W- W- C W+ W+ D B Observable: ratio of particle flow between the inter and intra-W regions: (A + B) / (C + D) CR models predict a modified particle flow in W+W- events:

  22. Results from particle flow CR Prob ‘Asymmetry’ from experiments combined in a c2 For SK1: Preferred value of the parameter (0.5 + 0.2 - 0.3) corresponds to dMW ~ 100 MeV!!

  23. Reduction of dMW DMW idea is to reduce effects by excluding particles situated outside angular cones around the jets. Some resolution is lost but systematic error is reduced. Good reduction factors are obtained for all available models Example: Cone (R=0.5 rad), with a statistical loss of ~ 25%: MW (GeV) ALEPH SK1 k=2.13 Cone radius (rad)

  24. mW from direct reconstruction 4q Non-4q Results in CERN-EP/2003-091, LEPEWWG/2003-02 still with standard jet algorithms DmW = 22 ± 43 MeV

  25.  errors as of summer 2003 errors expected for summer ‘05 conferences: there will also be an improvement on the beam energy error due to usage of LEP spectrometer. lots of hard work, and improved understanding … but diminishing returns

  26. Physics processes at LEP2 ~100k evts ~10k evts ~1k evts ~100 evts

  27. W-pair cross sections n exchange t channel ONLY

  28. n exchange and gWW vertex

  29. agreement to 0.6+-0.9% Clear proof of SU(2)xU(1) gauge couplings ! NB this is really non trivial. W3= Z cosqW + B sinqW

  30. LEPII (and LC) energy calibration Alas, beam polarization vanishes at LEP above E=65 GeV res. dep. will not work for linear collider idea: use e+e-  Z g to measure Ebeam given that mZ is so well known ALEPH

  31. Jets that are boosted lead to non trivial systematics! Tesla TDR  mW +- 6 MeV … hmmmm … the calorimeter and tracker will have to be very carefully designed, and full identification of final state hadrons (incl. neutrons, L and K) will be needed. This method gives a statistical error that matches that of the W mass measurement in the lvqq channel. using muons instead would require 20 times more stats. Systematic uncertainties Similar results by L3, OPAL

  32. TOP mass measurement CDF, D0 Status as of Moriond 2005 Method similar to mw at LEP II: form ‘estimator’ and compare measured distribution to templates with different top masses as input. (this cannot be done by rescaling since top is too narrow) Progress was noted when a ‘likelihood’ was built including event by event error estimate (D0, CDF) There is a flurry of new measurements and measurement techniques at RUNII. In most cases the limitation comes from the JET ENERGY CORRECTIONS.

  33. D0 Run I - Top Mass Analysis Using ME Method Top Mass determined using maximum likelihood • 91 candidate tt events • 77 with exactly 4 jets selected • 22 passing cut on background probability (Pbkg < 10-11) Expected statistical error pseudo-experiments • Nature429, 638-642 (2004) Expected 5.4 GeV Observed 3.6 GeV Jet energy scale syst: 3.3 GeV/c2 Mtop = 180.1 ± 3.6 (stat) ± 3.9 (sys) GeV/c2 Comparable precision to all previous measurements combined (some luck involved!)

  34. Mtop Measurements • Combined RunI mass: • mt=178.0 ± 4.3 GeV/c2 • was: 174.3 ± 5.1 GeV/c2 • Run II measurements • Systematic uncertainty largely dominated by jet energy correction: will be reduced • RunII goal is dm~2-3 GeV/c2 error bars: red=stat, blue=total

  35. Measuring Mtop Challenging: LO ME final state: • Lepton+jets • Undetected neutrino • Px and Py from Et conservation • 2 solutions for Pz from MW=Mln • Leading 4 jets combinatorics • 12 possible jet-parton assignments • 6 with 1 b-tag • 2 with 2 b-tags • ISR + FSR • Dileptons • Less statistics • 2 undetected neutrinos • Less combinatorics: 2 jets CDF sees: Largest uncertainty: Jet Energy Measurement

  36. Jet Energy Corrections Determine true “particle”, “parton” E,p from measured jet E, q Jargon: • Non-linear response • Uninstrumented regions • Response to different particles • Out of cone E loss • Spectator interactions • Underlying event but: top is NOT a color singlet, nor is tt pair. This method requires that the effect on the mass reconstructed using a specific jet rec. algorithm is perfectly modelled by the MC in a situation where there is no conservation law to prevent large effects. * There is no calibration of this! * (At LEP a light quark typically acquires 5-10 GeV due to fragmentation. This is not particularly well modelled in qqbar situation. But what about ppbar?)

  37. Color flow must be broken, but where? top top W (color singlet) b W (color singlet)

  38. and why not this? top top W (color singlet) b W (color singlet)

  39. top mass outlook Tevatron aims at measuring mtop with a precision of 2-3 GeV. This would be a remarkable achievement and progress. LHC hopes to be able to reach 1 GeV ATLAS note (SN-ATLAS-2004-040) mentions testing top mass against varying the jet cuts. Because of all the gluons around this may be a very sticky business!

  40. ELECTROWEAK fits (as of Moriond 2005) this in fact is a verification of the validity of the relation mW = mZ cosqW at tree level. (up to corrections due to mHiggs and any new physics cancellation)

  41. ELECTROWEAK fits (as of Moriond 2005) these plots show the fact that sin2qeffW i the most sensitive estimator of the Higgs mass, but the limitation will soon come from the top mass meast

  42. 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

  43. Constraints on mHiggs MH= 126+73-48 GeV MH  280 GeV @ 95% C.L.

  44. 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!

  45. Search for the SM Higgs Boson • Mass determines Higgs boson profile: @ 114 GeV : s ~ 0.1 pb BR(Hbb) ~ 74% BR(Htt) ~ 7% • SM searches exploited b-tagging extensively ALEPH 4-Jet candidate Mbb=114.3 GeV two b-tags

  46. SM Higgs: the final word from LEP Consistency with BG only hypothesis: Mass limit via CLS = CLS+B/CLB Mass spectrum after tight selection cuts Consistency with: • background only: 1-CLB = 0.09 @ 115 GeV (1.7s excess) • signal + background: CLS+B= 0.15 @ 115 GeV Observed Limit: 114.4 GeVExpected Limit: 115.3 GeV Phy. Lett. B565 (2003) 61

  47. Higgs at Tevatron? Ldt (fb-1) LEP Updated in 2003 in the low Higgs mass region W(Z)Hln(nn,ll)bb to include VBF  better detector understanding  optimization of analysis Tevatron Tevatron will begin sensitivity to LEP Higgs limit (or signal?) when >2.5 fb-1 will have been accumulated … it could be quite soon (Moriond 2007?)

  48. Higgs at LHC

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