Electroweak and Related Physics at CDF Tim Nelson Fermilab

1
W Charge asymmetry
Cigdem Issever, Adam Scott, and David Stuart UCSB
Preblessing, EWK 5/13/04

• CDF Note 6282, Measurement of W? en Charge
  Asymmetry
• CDF Note 6108, Alignment of the Plug Calorimeter
• CDF Note 6412, QCD Background for Plug Ws

2
Motivation

• W charge asymmetry arises from u(x)/d(x) in
  proton.
• Gives most sensitive u/d constraint at our x and
  Q2
• But still not well constrained at high x (high
  h).
• We dont already know the answer.
• Experimentally appealing.
• Can improve many of our forthcoming measurements.

3
Damn the ns. forward e ahead
Asymmetry in W production complicated by unknown
n pz
So, use lepton asymmetry
Which convolves production asymmetry with V-A
decay.
4
Damn the ns, forward e ahead
? Forward electrons with charge id are the key.
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Phoenix Tracking

• Two points and a curvature
• define a unique helix
• Primary vertex
• Shower Max cluster
• ET ? C

Attach hits using OI tracking
Select track with better c2/dof
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Phoenix Tracking
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Plug Alignment (CDF6108)
Align plug (actually PES) with COT tracks
allow offsets in x,y,z and a rotation in phi
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Plug Alignment
Measure and correct, iteratively from largest to
smallest f, x y, Z
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Internal Alignment
Residual misalignments attributed to internal
octant offsets
Fit for f and radial shifts in each octant.
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Consistent internals between bpel08 and bpel09
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Residuals look good after alignment
We performed various validity and systematic
checks and found it to be robust with small
systematics.
12
Charge ID
Incorrectly identifying the charge dilutes the
asymmetry. We can correct for it if we know the
rate, fQ? wrong / total
Atrue Ameas / (1-2fQ)
So make fQ small and measure it. MC predicts fQ
1. But MC doesnt know about residual
mis-alignments etc. We must measure it in data
and cannot assume any h dependence. Measured
fQ(h) with Z? ee-
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Z Event Selection
Baseline electron selection with COT or PHX
track. ETgt25 GeV PHX track is slightly
non-standard to optimize fQ. hits gt 4
c2 lt 8 Dc2 gt 0.5 Seed Pull lt 0.4
80ltmeelt100 and compare central Qtag
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Charge ID Measurement
CDFII Preliminary ?Ldt170/pb
fQCOT
fQPhx
h
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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Check kinematic distributions
CDFII Preliminary ?Ldt170/pb
Data MC
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Check kinematic distributions
CDFII Preliminary ?Ldt170/pb
Data MC
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Holy Phi
Data MC
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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
• 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
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Compare to COT when it is available
CDFII Preliminary ?Ldt170/pb
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Compare PDFs to data
CDFII Preliminary ?Ldt170/pb
CTEQ5L
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Compare PDFs to data
CDFII Preliminary ?Ldt170/pb
Overlay CTEQ3,4,5L, GRV98LO, MRSTd/u
CTEQ3,4 to 5 have less d/u from Run1 asym. We
keep pulling in Run2.
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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)
CDFII Preliminary ?Ldt170/pb
FMU
Compared to Run1 em
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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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A(h) with 25 lt ET lt 35 GeV
CDFII Preliminary ?Ldt170/pb
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A(h) with 25 lt ET lt 35 GeV
CDFII Preliminary ?Ldt170/pb
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A(h) with 35 lt ET lt 45 GeV
CDFII Preliminary ?Ldt170/pb
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A(h) with 35 lt ET lt 45 GeV
CDFII Preliminary ?Ldt170/pb
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Conclusion
W asymmetry provides new PDF constraints.