# Presentation: 526700

## W, Z and Drell-Yan Production II Asymmetries

- Susan Blessing
- Florida State University
- For the DØ and CDF Collaborations
- ICHEP 2006
- July 27, 2006

## Outline

- W production charge asymmetry
- W   (DØ) and W  e (CDF)
- direct method in W  e (CDF)
- Z  ee forward/backward asymmetry (CDF)
- Summary

## W boson production charge asymmetry

- u quarks typically carry more of a proton’s momentum than d quarks
- W+ goes in the proton direction
- W in the antiproton direction
- Use this difference to get information about the proton’s      u and d distributions – PDFs

- A(yW) =

## Q2, x reach 

- Traditionally, PDFs are
- measured in deep inelastic
- scattering – high energy
- electron-nucleon interactions.

- W asymmetry measurements:

- x = momentum fraction of parton
- Q2 = square of momentum transfer

- for |yW| < 2.5  (W  e, CDF

- 0.003 < x < 0.5

- for |yW| < 2  (W  , DØ)

- 0.005 < x < 0.3

- Q2, x coverage for CDF, DØ,
- HERA and fixed target experiments

## Lepton charge asymmetry

- W asymmetry difficult to measure
- neutrino longitudinal momentum
- Lepton pseudorapidity is available
- Lepton asymmetry is a combination of the W asymmetry and VA interaction from decay
- at higher lepton transverse momentum, VA contribution is smaller, A(yl) is larger
- at higher lepton rapidity, VA contribution is larger, A(yl) is smaller

- For all muon momenta

## W   (DØ) and W  e (CDF)

- W   (DØ) and W  e (CDF)

- W  

- W  e

- Tight selections to reduce charge and event misidentification

- CDF charge misid vs pseudorapidity

- PRD 71, 051104(R) (2005)

- Analyses done bin-by-bin

- DØ transverse mass distribution

## Asymmetry vs pseudorapidity

- PRD 71, 051104(R) (2005)

- W production and decay are CP invariant;
- fold the asymmetry to increase statistics.

## Asymmetry in ET bins (CDF)

- 25 < ET < 35 GeV
- 35 < ET < 45 GeV

- Improve correspondence between e and yW

- pZ ambiguity is a smaller
- effect for high-ET electrons

- For a given e, ET regions
- probe different ranges of yW (x); higher ET bin covers
- a narrower yW range

- PRD 71, 051104(R) (2005)

- Statistical and
- total uncertainties

## Direct W asymmetry method – CDF

- Reconstruct yW distribution

- W mass constraint

- Weight the two solutions

- Iterate since weight depends on yW

- cos*

- * = angle of charged lepton in W frame

- weight takes production and decay into account

## Projected uncertainties of direct method

- Compare expected statistical
- uncertainties in W asymmetry
- and lepton asymmetry with
- CTEQ6M error sets

- Direct method for W asymmetry
- measurement shows improved
- statistical uncertainty

- Estimated systematics are small

## Z  ee forward-backward asymmetry (CDF)

- Interference between (*) and Z exchanges

- Primarily * exchange below Z
- Z exchange at Z
- Z/ exchange above Z

- Interference depends on Mee

## AFB distributions

- Probe relative strengths of Z-q couplings;
- sensitive to u and d quarks separately

- Exchange of new particle(s) would alter AFB

- 500 GeV Z ́

- J.L. Rosner, PRD 54, 1078 (1996)

## Determining AFB

- Correct for background,
- acceptance/efficiency

- Since it’s a ratio, reduced systematics of luminosity, acceptances/efficiencies

- Acceptance is symmetric; distribution is not
- 	shifts AFB within a mass bin

- Event migration between bins
- 	large correlations between bins
- 	near Z pole

- Use a matrix based on MC
- events to “unfold” raw AFB
- distribution (correct for
- acceptance/efficiency and smearing)

- ISR and FSR

## Unfolded AFB distribution

- Agreement with LO SM calculation
- is 2/dof = 10.9/12

- No evidence for additional gauge bosons

- Updating to 1 fb1

- Can fit for quark and electron couplings
- Example using 72 pb1 result

**CDF: PRD 71, 052002 (2005)**
**Wichmann, HCP 2006**

## Summary

- Both DØ and CDF are measuring W and Z/ asymmetries

- Both experiments have significantly more data available,
- over 1fb1, and are making progress on extending these
- analyses to include this data.

## Backup Slides

## Lepton asymmetry and pT cut

## DØ overall efficiency ratio

- Overall efficiency ratio = product of individual ratios

- 2/dof = 0.71

- L2 muon trigger efficiency
- L3 track trigger efficiency
- Offline muon reconstruction efficiency
- Offline tracking efficiency

## DØ charge misidentification

- 1. Only isolated muons

- 2. Plus hits in the tracker

- 3.  Plus additional 2/dof

- 4.  dca but no 2

- Cross checks
- no Z invariant mass cut
- reduced muon pT cut
- use other triggers
- study misid in GEANT MC
- No difference

- Sample of 10,000 ee events.
- After all selection cuts,
- only one same-sign
- event remains.

- Charge misid rate = (0.010.01)% for ≤ 1.0
-                                  (0.01±0.05)% for  1.0

- inflate uncertainty at
- high  due to low statistics

## DØ systematic uncertainties

- Data
- differences in efficiencies for  and 
- take        = 1.0 and use uncertainty as a systematic
- charge misidentification

- Background
- PMCS modeling of EW backgrounds
- muon energy in calorimeter
- hadronic energy scale (ET)
- uncertainty in signal isolation efficiency
- uncertainty in background isolation efficiency

- 

- Vary everything by ±1,
- use change in asymmetry as uncertainty.

## DØ magnet polarities

- Solenoid polarities

- Toroid polarities
- Data is 50.7% : 49.4%

## W   (DØ) and W  e (CDF)

- W  

- Z  
- Z   
- W   
- QCD multijet

- W  e

- PRD D 71, 051104(R) (2005)

- Z  ee
- W   e
- QCD multijet

- Analyses done bin-by-bin

## DØ folded asymmetry plot

- Red curve:  CTEQ6.1M central value
- Blue curve:  MRST02
- Combined uncertainties.

## CDF W asymmetry weighting

## CDF Z → ee mass distributions

- High mass region

- Low mass region

## CDF AFB background