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W Mass Measurements and Electroweak Constraints

W Mass Measurements and Electroweak Constraints. Happy 22 nd Birthday W’s UA1,UA2 LEP RIP W Boson Properties WW xsec, W BRs, V cs , TGCs W Mass  Higgs mass The Future TeVatron Run II, LHC, ILC. Chris Parkes.

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W Mass Measurements and Electroweak Constraints

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  1. W Mass Measurements and Electroweak Constraints • Happy 22nd Birthday W’s • UA1,UA2 • LEP RIP • W Boson Properties • WW xsec, W BRs, Vcs, TGCs • W Mass  Higgs mass • The Future • TeVatron Run II, LHC, ILC Chris Parkes Higgs Maxwell Particle Physics Workshop, Ne-SC Edinburgh, February 9th 2005

  2. W Discovery • UA1, UA2 1983 UA2, Phys.Lett.B276:354-364,1992 MW=80.350.330.17 GeV

  3. LEP’s Legacy – Weighing the Bosons • Precision measurements of the weak interactions • The Z • LEP 1 Phase 1989-1995 • 15 million Z’s • MZ = 91187.52.1 MeV • 2 parts in 105 ! • Z=2495.22.3 MeV

  4. LEP 2 Phase 1996-2000 • W boson measurements • Measuring the Higgs mass ? • MW depends on (mtop)2 • MW depends on ln (mhiggs)

  5. WW Production at LEP • Three Feynman graphs with interference gives Six terms • Only Born level shown • Near threshold t-channel dominates • Cancellations are consequence of SM structure

  6. First WW Event • 35,000 selected WW’s at LEP2 • Luminosity ~700pb-1per Experiment • Energies 161 – 209 GeV

  7. Event Selection Divide events into final states: • Event characteristics: • Jets, leptons • Backgrounds • Z, ZZ • Selections typically: • Neural Net, Likelihood • based

  8. WW cross-section results Final DELPHI, ALEPH, L3 • Measured cross-sections corrected for QM interference with other processes that produce the same final state • Theoretical error at threshold (IBA) 2% • Theoretical error above 170 Gev (LPA/DPA) 0.70.4% GENTLE 0.969 0.009

  9. Branching Ratios, Vcs q W |Vqq’|2 q’ SM 67.51% Assuming measurements of other elements • 2.8 sigma excess in tau decays

  10. W Mass Analysis Technique • Select Events • Reconstruct lepton and jets (also gluon jets) • Impose Kinematic constraints • improve resolution • E,p conservation • M1,M2 or M1=M2 • Perform maximum likelihood fit to data • Calibrate with simulation • Event by Event Resoultion

  11. LEP W Mass Error Components Statistics FSI EBeam Detector Hadronisation O()

  12. LEP Beam Energy Determination Correlated between all experiments • Spin precession frequency of polarised e+e- beams (EBEAM=200keV) • Polarisation< 60 GeV Calibrate other methods • Measurement of magnetic field of LEP bending magnets • Oscillations of beam around ideal orbit (Synchotron tune) • Spectrometer From Ebeam

  13. Final State Interactions • W+W- decay vertices separation typically 0.1fm • Typical hadronisation scale 1fm • BEC: between final state hadrons – • identical bosons (pions) close in phase space – 35 MeV • CR: cross-talk between coloured objects in non-perturbative QCD region – 65 MeV • Additional systematic on W Mass for fully-hadronic decays • Simulation • Measurements

  14. World average W Mass • Weight of qqqq channel in LEP fit 10% • Mass difference (no FSI) 2243 MeV • Stat (no syst.) 21 MeV • LEP direct determination of W Width • 2.150  0.0068(stat.) 0.0060(syst.) GeV [0.029(stat.) 0.031 (syst)]

  15. Measuring the Higgs Mass Remember LEP 1 predicted the top mass ! mHiggs < 260 GeV (95% CL)

  16. SUSY? • SM MH varied • MSSM parameters varied

  17. Triple Gauge Couplings Also QGCs!(WW) And NTGCs • O(em): • 1-2% xsec • W- production angle becomes more fwd peaked C, P conserving emag. gauge invariant WWZ, WW

  18. The near-ish Future: TeVatron, LHC • LEP+TeVatron Run II MW~30 MeV • LHC MW~15 MeV • Transverse mass • No knowledge of longitudinal  momentum • Transverse  momentum from missing momentum CDF • Systematics limited Statistical Error 2 MeV for 10fb-1 • Lepton energy scale, use Zl+l- i.e. measure mW/mZ • Parton distribution functions W longitudinal plepton acceptance

  19. The Far Future: ILC Measure the cross-section at threshold measure mass Measurement made at LEP with 10pb-1 Sensitivity ~ same at direct reconstruction • MW~7MeV The difficulties: • Luminosity • LEP 700pb-1 • ILC 107 s, 100fb-1 • Determine Background • At threshold t-channel •  diagram, eL+ eR- • Polarised beams can turn off signal ! • Theory: • To obtain error of 1MeV • GENTLE MW=24MeV • Full O() calculation in threshold region,~ 104 Feynman graphs • Ebeam • Spectrometer, calibrate to Mz • Z radiative return

  20. Dear All,Having a lovely time in the 2nd nicest town in Scotland. The standard model Higgs is light mHiggs < 260 GeV (95% CL) • WW cross-section, ±1% • BR, Vcs • TGCs • W Width 2.150 0.091 GeV • W Mass 80.4120.042 GeV Given the state of the British postal service, it may be measured to ~15 MeV(LHC) , ~7 MeV (ILC) by the time this arrives …

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