Forward Backward Asymmetry using Di-electrons at CDF

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Forward Backward Asymmetry using Di-electrons at
CDF

• Gregory Veramendi (UC Berkeley / LBNL),
• Adam Gibson (UCB/LBNL), Young-Kee Kim (UofC)
• (on behalf of the CDF Collaboration)

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AFB

• Interference between Z and g exchanges
• q-dependent cross sections
• ds / dcosq A(1cos2q) Bcosq
• AFB 3B / 8A
• Direct probe of couplings
• Measure parameters of S.M sin2?W
• Sensitive to new Physics Z
• Reduces systematics

g
Z
f e, quarks

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Previous Measurements
hadron colliders
ee- colliders
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AFB Analysis Outline

• Selection
• 2 high PT isolated electrons
• ET gt 20 GeV

• Outline
• Selection
• Background
• Acceptance
• Results

e
Z/g
e-
72pb-1
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Calculating Asymmetry

• Calculating AFB

• cos? in Collin-Soper frame
• Minimize ambiguity in the incoming quark Pt
• cos?gt0 ?Forward
• cos?lt0 ?Backward

lab frame
Z0/g
PZ 0
Z-Axis
Z0/g
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QCD Backgrounds
CDF Run II Preliminary

• QCD dijet dominant
• Estimate from data
• Central Track Curvature
• Assume QCD charge symmetric
• Same sign events
• Remove tridents
• Forward
• 128 65 events

CDF Run II Preliminary
21.5 5.9 events
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Characteristics of QCD

• Is QCD-AFB symmetric?
• QCD enriched sample
• same kinematic and fiducial cuts

• Invariant mass distribution
• Pythia dijet events
• generator level with
• energy smearing

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Backgrounds
CDF Run II Preliminary

• Non-QCD
• Estimate from MC.
• Take into account their AFB in background
  subtraction.

W W
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Cos? Distributions
Raw Distr.
Acceptance

• Grey
• No Cut
• Yellow
• ?1,2 lt3
• Blue
• ?1 lt1,?2 lt3
• Green
• ET gt 20 GeV

Low Mass
Pole Region
High Mass
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Acceptance w/ Simulation

• Correcting for
• Energy resolution
• Kinematic and fiducial cuts
• Radiation from FSR and external brems
• Electron ID efficiency
• Numerator analysis cuts
• Denominator generator level w/o QED FSR

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Drell-Yan Mee line shape
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AFB Conclusions

• Past measurements (ee- and hadron colliders)
  have been essential in confirming SM.
• Tevatron Run IIa
• Difficult to improve measurements with M lt 200
  GeV (LEP-II energies).
• AFB with M lt 200 GeV consistency check
• AFB interests are with M gt 200 GeV
• Run IIa data so far similar to Run I
• Run I meas. showed 2s deviation at 400 GeV.
• Dont see deviations at high mass.