Diapositiva 1

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Deep Inelastic Scattering 2006
EWK Results _at_ Tevatron
20th April 2006
Jose E. Garcia - INFN PISA for the CDF and DØ
Collaborations
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Outline

• W and Z production
• Motivation
• W, Z cross section
• W and Z asymmetries
• Diboson production
• WZ and WW
• Anomalous couplings
• Summary
• Measurements shown here use ?Ldt ? 0.1 to 0.8
  fb-1

The Tevatron Accelerator
Peak luminosity 1.8 1032 cm-2s-1 Recent
Integrated luminosity per week ? 25 pb-1 CDF and
DØ ? 1.2 fb-1
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CDF and DØ in RUNII

• Both detectors
• Silicon vertex tracker
• Solenoid
• High rate trigger/DAQ
• Calorimeter and muons

CDF

• Silicon tracking system in 1.4T magnetic field.
• Lead (iron) scintillating EM (Had) Calorimeter.
• Forward end-plug calorimeter, ? 3

Silicon and fiber tracker in 2T magnetic
field Liquid argon/uranium calorimeters Muon
coverage up to ? 2
DØ
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ElectroWeak Analyses

• Motivation
• Test the Standard Model (precise measurements)
• Provide evidence of physics beyond SM
• Important input to LHC physics program
• Signatures at hadronic colliders W and Z bosons
  decaying hadronically are overwhelmed by direct
  multiple jet production.
• Identification through leptonic decays

W/Z
2 isolated leptons with opposite charge
isolated lepton and ET
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Z ? ??

• Detection through two high pT muons (CDF,DØ)
• ? lt 1 (2)
• Two muons with pT gt 20 (15) GeV
• Background dominated by
• QCD jets into semi-leptonic decays of bb and Z???

14352 Candidates

• Data

337 pb-1 updated
148 pb-1
66 GeV
116 GeV
Narrow peak high resolution of CDF tracking
system
Large number of events due to higher acceptance
of muon DØ system
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W in forward region
Extension of electron ID to forward region of
detector ? 1.2 lt?lt 2.8. Complementary to
central result
Used combined information from forward EM
calorimeters and extended tracking system (ISL)
CDF
CDF Run II Preliminary
223 pb-1 updated
48144 W candidates
? 4.5
?0.07
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Cross Section Summary
Tevatron W ? l ? cross sections
Tevatron Z ? l l- cross sections
Run II
Run II
Run I
Run I

• consistent and in good agreement with NNLO
  theoretical calculations
• uncertainties dominated by luminosity ? 6
• accuracy limited by systematic effects
• lepton-id ? 1 - 3 ( ? 3 - 4 for ?s)
• PDF ? 1 - 2

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W Charge Asymmetry
Use Ws to probe the proton structure

• u quark inside proton carries higher fraction of
  momentum than d.
• W production is sensitive to u and d PDF.

anti-proton
proton

• Observable quantity is lepton rapidity
• Convolution of W production asymmetry and V-A
  decay
• W charge asymmetry provides new PDF constraints

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W Charge Asymmetry (II)

• New DØ result in W??? channel
• increased acceptance up to ? 2 (forward
  triggers)
• require single isolated muons
• Measurement statistically limited
• Charge identification is crucial
• Misidentification probability is 0.01 for ? ?
  2
• CP folding to provide better statistical
  uncertainties

DØ Run II Preliminary
DØ Run II Preliminary
230 pb-1 new
230 pb-1 new
Asymmetry
Asymmetry
MRST02 PDF central value CTEQ6.1M PDF
uncertainties
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Z / ? ? ee Asymmetry - AFB

• Interference between Z and ? exchanges
• Vector and Axial-vector gives rise to an angular
  asymmetry
• d? / dcos? A(1cos2?) B cos? ? B ? 0
  introduces asymmetry
• Direct probe of V and A couplings
• New particles would change AFB
• AFB depends on mass

Consistent with SM ? ?/ndof with respect to SM
is 10.9/12
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Di-boson Studies

• Diboson production
• Test Triple Gauge Couplings
• Tevatron explores higher s than LEP
• New physics probe
• Background to different analyses, important
  knowledge for LHC
• Signatures
• High pT leptons
• Electron or muon with PTgt20-25 GeV
• Isolated ET(?R 0.4) lt 0.1 ET(l)
• Large missing ET ET gt 20-25 GeV

H,X
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WZ Production

• Sensitivity to the WWZ vertex coupling
• Unavailable at ee- colliders
• Clean tri-lepton signature (no other SM process)
• Z selection
• 2 high pT leptons and M(ll) MZ
• W selection
• Isolated high pT lepton and Missing ET
• Backgrounds Z / ? jet

W
W
Z
320 pb-1
825 pb-1 updated
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WW Production

• Important for Higgs searches
• Test self interaction of heavy bosons
• Probe for new heavy bosons
• Selection
• 2 high pT leptons and Missing ET
• Backgrounds
• Drell-Yan, Z / ? jet, tt and Heavy bosons
  (WW,ZZ)

X
252 pb-1
Events / 2 GeV
Missing ET (GeV)
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W W/Z ?W(lep) W/Z(had)

• Larger yield than fully leptonic decays
• Lepton gives trigger to events
• Selection
• Lepton ET gt 25 GeV, ? lt 1
• ET gt 25 GeV
• At least 2 jets ET gt 15 GeV and 32 lt M(jj) lt 184
  GeV

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WW/Z ?W(lep) W/Z(had)

• Main systematic contributions
• W 2 jets cross section (20 uncertainty)
• W 2 jets LO is sensitive to renormalization
  scale
• Jet energy scale (10 uncertainty)
• Several methods checked to perform the
  measurement
• Fit signal background shape to data
• Use sidebands in data to check MC

Expectations
Fit to data
350 pb-1 new
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WW/WZ Anomalous couplings

• Anomalous Couplings (AC) can be tested in the
  WW/WZ production
• W transverse momentum is found to be the best
  observable to test AC
• AC parameterized considering
• with ?? 0 and ? 0 SM is obtained.
• pT(W) spectrum fitted for each AC hypothesis ?
  Set limits to ?? and ?

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• Some of the latest analyses have been shown
• Tevatron EWK measurements increase their
  precision up to few
• New values for W/Z production using more
  statistics
• Results agree with the SM predictions
• Di-boson analyses
• Better limits have been established to di-boson
  production
• New decay channels are studied WW/WZ with jets
  in the final state.
• Limits obtained for AC already better than in
  RUN I

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Deep Inelastic Scattering 2006
BACKUP
20th April 2006
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Tevatron Accelerator
Tevatron Collider is operating successfully Tevat
ron delivered ?Ldt ? 1.6 fb-1 ? 1.2 fb-1 in tape
per experiment
Peak luminosity 1.8 1032 cm-2s-1 Integrated
luminosity per week ? 25 pb-1 CDF and DØ ? 1.2
fb-1
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Z ? ?e ?h

• Use channel ?1 ? e ?2 ? had
• detect hadronic ?s as narrow, isolated
  calorimeter clusters matched to tracks
• Invariant mass of the system (?0
  track-calorimetric cluster) should be consistent
  with ? mass
• Requirements
• isolated electrons (ET(e) gt 10 GeV)
• hadronic ? (ET(?) gt 10 GeV) and ?? lt 1.0
• impose event topology cuts to suppress QCD and
  Wjets backgrounds

CDF Run II Preliminary
CDF Run II Preliminary
504 events
504 events
350 pb-1 new
350 pb-1 new
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W Mass Measurement
W propagator includes H, tb and hypothetical new
particle loops.
?MW 34 MeV
Precise knowledge of MW constrains SM MH, as well
as hypothetical new particles.

• Tevatron Run II has now 6 times Run I CDF, DØ
  data sets. CDF has analyzed first 200 pb-1 of
  data and determined uncertainties. Run II goal is
  to reduce uncertainty to less than 40 MeV.
• LEP 80,447 ? 42 MeV
• Tevatron 80,454 ? 59 MeV (Run I)

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W Mass Measurement

• W mass is obtained from transverse mass (MT)

Simulation
NLO event generator Model detector effects
Detector Calibration
Calorimeter energy scale Tracking momentum scale
W Mass templates Backgrounds
DATA
Binned likelihood fit
W Mass
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W Mass Measurement

• Z events are used for tuning and cross-checks ?
  model recoil energy and to calibrate the lepton
  resolution

• Muon momentum scale is determined to 3 parts in
  10,000 using J / ? and ?(1s) decays.

CDF RUN II PRELIMINARY

• Use calibrated tracks to set calorimeter
  electromagnetic energy scale E/p peak in W
  events.

CDF RUN II PRELIMINARY
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W Mass Measurement

• Using 200 pb-1 of Run II data CDF estimated the
  uncertainty on MW

Total uncertainty 76 MeV (e? combined) already
lower than CDF Run I (79 MeV)
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