C. K. MackayEPS 2003

1
Electroweak Physics and the Top Quark Mass at
the LHC

• Kate Mackay
• University of Bristol
• On behalf of the Atlas CMS Collaborations
• EPS Aachen, July 2003

2
Outline

• The Atlas and CMS Detectors
• W Mass
• Measurement of the W mass
• Errors on W mass measurement
• Top Physics
• Top Quark Mass measurements
• Errors on top mass measurement
• Single top quark production
• Triple Gauge Boson Couplings
• WW?
• ZZ? and Z??
• Summary

3
The Atlas Detector

• Inner Detector
• Silicon pixels and strips
• Transition radiation tracker
• EM Calorimeter
• Sampling Pb/LAr
• Hadron Calorimeters
• Barrel Fe/Scintillating tiles
• Endcaps Cu W /LAr
• Muon Spectrometer
• Drift tubes Cathode strip
• Tubes, resistive plate chambers
• Magnet 2T Solenoid

4
The CMS Detector

• Inner Detector
• Silicon pixels and strips
• Preshower
• Lead and silicon strips
• EM Calorimeter
• Lead Tungstate
• Hadron Calorimeters
• Barrel Endcap
• Cu/Scintillating sheets

5
Precision of the W Mass

• The W mass is known with a precision of
• 34 MeV from LEP2 and the Tevatron -
• What is the motivation for improving
• at the LHC?
• Higgs mass estimation
• Radiative corrections
• For equal weights in a ?2 test
• If ?Mt 2 GeV at the LHC, we require
• ??MW 15 MeV

• W Transverse Mass Distribution including
• expected detector resolution

Measurement of the W mass is performed in the
leptonic channels using the transverse mass
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Precision of the W Mass

• Cuts
• Isolated charged lepton pT gt 25 GeV ? lt 2.4
• Missing transverse energy ETMiss gt 25 GeV
• No jets with pT gt 30 GeV
• Recoil lt 20GeV
• Sources of Uncertainty
• Statistical uncertainty
• pp ? W X ? 30 nb (l e,?)
• W ? l?l 3 x 108 events
• lt 2MeV for 10 fb-1
• Systematic Error
• Detector performance
• Physics

Source ?MW (MeV)
Statistics ? 2
E-p scale 15
Energy resolution 5
Recoil model 5
Lepton identification 5
pTW 5
Parton distribution functions ? 10
W width 7
Radiative decays 10
Background 5
Total ? 25
? Reduces the error on log MH from 0.2 to 0.1
1 year, 1 lepton species ? 25 MeV Combining
lepton channels ? 20 MeV Combining
experiments ? 15 MeV
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Top Mass

• Together with MW helps to constrain the SM Higgs
  mass
• tt production main background to new physics
  processes production and decay of Higgs bosons
  and SUSY particles
• Top events used to calibrate the calorimeter jet
  scale
• Precision measurements in the top sector provide
  information of the fermion mass hierarchy

• At low luminosity
• Semi-leptonic best channel for top mass
• measurement (pure hadronic channel can
• also be used)
• Error dominated by systematic errors
• Jet energy scale
• Final state gluon radiation

-
tt leptonic decays (t ?bW)
Single lepton W ? l?, W ? jj 29.6 2.5 x 106 events
Di-lepton W ? l?, W ? l? 4.9 400,000 events
-
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Top Mass Measurements

• Predicted error on the top mass measurement from
  the semi-leptonic channel of ? 1.3 GeV
• (Di-leptonic channel ? 2 GeV)

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Single Top Quark Production

• Probe the t-W-b vertex
• Direct measurement of the CKM matrix element Vtb
• ?(t) ? Vtb
• New Physics heavy Vector Boson W
• Source of high polarized tops
• Background tt-, Wbb-, Wjj
• Tevatron ?(t) ?(t-)
• LHC ?(t) 1.5 ?(t-)
• ? LHC provides a new scenario for
• single top quark production.

• ? (pb) D0 CDF LHC
• ?Wg lt22 lt13 245
• ?Wt - - 60
• ?W lt17 lt18 10
• For each process ? ? Vtb2
• Systematic errors
• B-jet tagging, luminosity, theoretical
• (dominates Vtb measurements)

Process S/B S/vB ?Vtb/Vtb Statistical ?Vtb/Vtb Theory
W-g 4.9 239 0.51 7.5
Wt 0.24 25 2.2 9.5
W 0.55 22 2.8 3.8
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WW? Vertex

• Parameters ?? and ?? are related to
• physical properties of the W boson.
• They are CP-conserving couplings and
• relate to the electric quadrupole
• moment of the W (QW) and its
• magnetic dipole moment (?W)
• In the SM ?? 1 (? ?? 0) and ?? 0 at
• tree level.
• Anomalous contribution is enhanced
• at high vs

• Observing the anomalies
• pT ? distribution
• Radiation zero ??(?,l)
• MT distribution
• Angular distribution ?W

• Shaded SM
• Clear ?? 0.01

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Limits on W?

• pT Cuts (?) gt 100 GeV, (l) gt 25 GeV,
• pT miss gt 50 GeV
• Jet veto
• ?R(?,l) gt 0.7
• MT (l ?,pT miss) gt 90 GeV

• LHC Limits for 10 fb-1 and 100 fb-1

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ZZ? Z?? Vertices

• Anomalous couplings are hVi (i 1-4, V
• Z, ?)
• hV3 and hV4 are the CP-conserving couplings
• and hV1 and hV2 are the CP-violating couplings
• relating to the transition moments of the Z

• Observing the anomalies
• pT ? distribution
• MT distribution

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ZZ? Z?? Vertices

• Main Backgrounds
• Z Jet
• Z ???
• Cuts
• ??,l lt 2.4
• pT? gt 100 GeV
• pTl gt 25 GeV
• ?R(?,l) gt 0.7
• MT (ll?) gt 100 GeV

• Predicted Limits
• ? 1 TeV
• ? 3 TeV
• Typically order of magnitude improvement

hZ3 hZ4
10 fb-1 2.0 x 10-2 8.2 x 10-4
100 fb-1 7.8 x 10-3 3.6 x 10-4
hZ3 hZ4
10 fb-1 2.3 x 10-3 1.9 x 10-5
100 fb-1 1.5 x 10-3 8.5 x 10-6
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Summary

• LHC precision measurements, unexplored kinematic
  regions, high-statistics (W, Z, b, t factory)
• W Mass Measured with a precision of 15 MeV
• (Combining lepton channels and both Atlas and
  CMS)
• Top Mass Measured with a precision of 1.3 GeV
• ? Higgs Mass
• Together ?MW and ?Mt improve error on log MH
  50.
• Triple Gauge Couplings
• WW? Anomalies clearly observed in pT(?)
  distribution
• ZZ? Anomalies clearly observed in pT(?) and
  MT(ll?) distribution
• Predicted Limits order of magnitude improvement