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W Charge asymmetry. Cigdem Issever, Adam Scott, and David Stuart UCSB. Preblessing, EWK 5/13/04. CDF Note 6282, Measurement of W  e n Charge Asymmetry CDF Note 6108, Alignment of the Plug Calorimeter CDF Note 6412, QCD Background for Plug Ws. Motivation.

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slide1

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
slide2

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 don’t already know the answer.

Experimentally appealing.

Can improve many of our forthcoming measurements.

slide3

Damn the n’s. forward e ahead

Asymmetry in W production complicated by unknown n pz

So, use lepton asymmetry

Which convolves production asymmetry with V-A decay.

slide4

Damn the n’s, forward e ahead

 Forward electrons with charge id are the key.

slide5

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

plug alignment cdf6108
Plug Alignment (CDF6108)

Align plug (actually PES) with COT tracks:

allow offsets in x,y,z and a rotation in phi

slide8

Plug Alignment

Measure and correct, iteratively from largest to smallest

f, x & y, Z

slide9

Internal Alignment

Residual misalignments attributed to internal octant offsets

Fit for f and radial shifts in each octant.

slide11

Residuals look good after alignment

We performed various validity and systematic checks

and found it to be robust with small systematics.

slide12

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 doesn’t know about residual mis-alignments etc.

We must measure it in data and cannot assume any h dependence.

Measured fQ(h) with Z e+e-

slide13

Z Event Selection

Baseline electron selection with COT or PHX track. ET>25 GeV

PHX track is slightly non-standard to optimize fQ.

# hits >= 4

c2 < 8

Dc2 > 0.5

Seed Pull < 0.4

80<mee<100 and compare central Qtag

slide14

Charge ID Measurement

CDFII Preliminary ∫Ldt=170/pb

fQCOT

fQPhx

h

Errors calculated with Bayesian prescription, CDF5894.

slide15

W Event Selection

Baseline electron selection w/ PHX track.

ET>25 GeV

Missing ET > 25 GeV

50 < MT < 100 GeV/c2

No other EMO with ET>25 GeV

to suppress QCD and DY

slide16

Check kinematic distributions

CDFII Preliminary ∫Ldt=170/pb

Data

MC

slide17

Check kinematic distributions

CDFII Preliminary ∫Ldt=170/pb

Data

MC

slide18

Holy Phi

Data

MC

slide19

Raw Asymmetry

CDFII Preliminary ∫Ldt=170/pb

Curve is just a fit to guide the eye.

slide20

Raw Asymmetry

CDFII Preliminary ∫Ldt=170/pb

Curve is just a fit to guide the eye.

slide21

Background

  • We correct the asymmetry for backgrounds from:
    • W tn  enn
    • Asymmetric, measured from MC
    • Z e+e-
    • Asymmetric, measured from MC
    • QCD
    • Symmetric, measured from data CDF 6412.
  • Use Iso vs MET.
slide22

QCD Background systematic

  • Check assumption of non-correlation
  • small systematic, as long as we don’t use the

PEM 3x3 c2 or 5x9 cuts (they are correlated with Iso)

 upper limit by about a factor of 2.

slide23

QCD Background

CDFII Preliminary ∫Ldt=170/pb

QCD fraction

h

We use 0.5 ± 0.25. Becomes significant for h >1.8

slide24

Corrected Asymmetry

CDFII Preliminary ∫Ldt=170/pb

slide25

Compare to COT when it is available

CDFII Preliminary ∫Ldt=170/pb

slide26

Compare PDFs to data

CDFII Preliminary ∫Ldt=170/pb

CTEQ5L

slide27

Compare PDFs to data

CDFII Preliminary ∫Ldt=170/pb

Overlay CTEQ3,4,5L, GRV98LO, MRST+d/u

CTEQ3,4 to 5 have less d/u from Run1 asym. We keep pulling in Run2.

slide28

CP check

CDFII Preliminary ∫Ldt=170/pb

slide29

A(|h|)

CDFII Preliminary ∫Ldt=170/pb

slide30

A(|h|)

CDFII Preliminary ∫Ldt=170/pb

FMU

Compared to Run1 e+m

slide32

Getting more sensitivity to AW

35 < ET < 45

25 < ET < 35

slide33

A(h) with 25 < ET < 35 GeV

CDFII Preliminary ∫Ldt=170/pb

slide34

A(|h|) with 25 < ET < 35 GeV

CDFII Preliminary ∫Ldt=170/pb

slide35

A(h) with 35 < ET < 45 GeV

CDFII Preliminary ∫Ldt=170/pb

slide36

A(|h|) with 35 < ET < 45 GeV

CDFII Preliminary ∫Ldt=170/pb

slide37

Conclusion

W asymmetry provides new PDF constraints.

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