W Charge Asymmetry

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W Charge Asymmetry

• Cigdem Issever, Adam Scott and David Stuart
• UCSB

• CDF-Note 6282, Measurement of the W-gte nu Charge
  Asymmetry
• CDF-Note 6108, Alignment of the Plug Calorimeter
• CDF-Note 6412, QCD Background of Plug Ws

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W Charge Asymmetry
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W Charge Asymmetry
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Essentials for W Charge Asymmetry

• Plug electron identification with Phoenix
  SiTracking
• Plug and Silicon
• Charge determination

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Charge ID
Charge determination critical. Charge
misidentifation fqwrong/total dilutes the
asymmetry. Correct for it Atrue
Ameas/(1-2fq) So, make fq small and measure
it. MC predicts fq 1. But MC has no residual
mis-alignments, etc--gt We must measure fq in
data. Measured fq(eta) with Z-gte e-
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Z Event Selection

• Baseline electron selection with COT or Phoenix
  Track and Etgt25GeV.
• Phoenix Track selection optimized for small fq
• SiRPhiHits gt 4
• Chi2 lt 8
• Delta Chi2 gt 0.5
• Pull lt 0.4
• (Chi2_Seed/dof for track with
  lesser Chi2_total/dof)
• (Chi2_Seed/dof for track with
  greater Chi2/dof)
• 80 lt Meelt100 GeV and compare central Qtag

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Mee Distribution
CDFII Preliminary ?Ldt170/pb
CDFII Preliminary ?Ldt170/pb
Central
Plug
Data (west, east) MC
Corrected energy scale in MC
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Charge Mis-ID Rate
CDFII Preliminary ?Ldt170/pb
fqPHX
fqCOT
Errors calculated with Bayesian prescription
CDF5894
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W Event Selection
Baseline electron selection w/ PHX track.
ETgt25 GeV Missing ET gt 25 GeV 50 lt MT lt 100
GeV/c2 No other EMO with ETgt25 GeV to
suppress QCD and DY
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Kinematic Distributions MT and ET
Data (west, east) MC
CDFII Preliminary ?Ldt170/pb
Central
Plug
Plug
Central
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Kinematic Distributions MET and h
CDFII Preliminary ?Ldt170/pb
Data (west, east) MC
Plug
Central
h
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Kinematic Distributions f
CDFII Preliminary ?Ldt170/pb
Data MC
Central
f
Plug
f
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Raw Asymmetry
CDFII Preliminary ?Ldt170/pb
Curve is just a fit to guide the eye.
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Raw Asymmetry
CDFII Preliminary ?Ldt170/pb
Curve is just a fit to guide the eye.
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Background

• We correct the asymmetry for backgrounds from
• W ? tn ? enn (trippled statistic)
• Asymmetric, measured from MC
• Z? ee-
• Asymmetric, measured from MC
• QCD
• Symmetric, measured from data CDF 6412.
• Use Iso vs MET.

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QCD Background systematic

• Check assumption of non-correlation
• small systematic, as long as we dont use the
• PEM 3x3 c2 or 5x9 cuts (they are correlated
  with Iso)
• ? upper limit by about a factor of 2.

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QCD Background
CDFII Preliminary ?Ldt170/pb
QCD fraction
h
We use 0.5 0.25. Becomes significant for h gt1.8
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Corrected Asymmetry
CDFII Preliminary ?Ldt170/pb outer error bars
total error inner error bars statistical error
Band correlated error from Energy scale
uncertainty
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CP Check
CDFII Preliminary ?Ldt170/pb
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A(h)
CDFII Preliminary ?Ldt170/pb
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A(h)
FMU
Compared to Run1 em
CDFII Preliminary ?Ldt170/pb
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Getting more sensitivity to AW
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Getting more sensitivity to AW
35 lt ET lt 45
25 lt ET lt 35
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AW for 25 lt Et lt 35 GeV
CDFII Preliminary ?Ldt170/pb
Band correlated error from Energy scale
uncertainty
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AW for 35 lt Et lt 45 GeV
CDFII Preliminary ?Ldt170/pb
Band correlated error from Energy scale
uncertainty
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AW(h) with 25 lt ET lt 35 GeV
CDFII Preliminary ?Ldt170/pb
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AW(h) with 35 lt ET lt 45 GeV
CDFII Preliminary ?Ldt170/pb
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AW(h) for different ET ranges
CDFII Preliminary ?Ldt170/pb
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Conclusion

• We measured the W Charge Asymmetry
• Provides new PDF constraints

CDFII Preliminary ?Ldt170/pb
CDFII Preliminary ?Ldt170/pb
Joey Huston, CTEQ6.1 (ResBos NLO,NLL)
Higher Pt prediction indicates that data has more
pdf discrimination