W/Z Results from CDF

Dave Waters

University College London

Inclusive Cross-Section Measurements

R(W/Z)

R(W/Z) : New Ideas

W Charge Asymmetry

W Charge Asymmetry : New Ideas

Other W/Z Measurements

[ W Mass  Ashutosh ]

CTEQ/CDF/D0 W/Z Workshop

Inclusive W/Z Cross-Section Measurements

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e/m : 2% systematics limited cross-section measurements (w/o correlated L uncertainty)

Dominant systematics : acceptance (PDF's); efficiency.

Benchmark measurements for all high PT lepton analyses.

Inclusive W/Z Cross-Section Measurements

e,  combined

correlated systematics fully taken into account

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R(W/Z)

SM : 226.4  0.3 MeV

SM : 3.361 

LEP

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Branching Ratios

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BUT :

Universality Tests

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[ similar to LEP ]

R(W/Z) 72pb-1 : Closer Look at Major Systematics

acceptance

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R(W/Z) : New Approach

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Select W's & Z's with identical cuts.

Single lepton only must pass trigger and full lepton ID requirements.

Fit the lepton pT(), ET(e) spectra to obtain the relative W & Z fractions.

K. Copic (U Mich.); V. Martin, M. Schmitt (NWU)

W

Z

l

l



l

R(W/Z) : New Approach

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Efficiencies :

Single lepton requirement virtually eliminates efficiency differences between W's and Z's.

Backgrounds :

QCD background reduced with a hadronic recoil cut (made similar for W's & Z's by looking for “loose” second leptons)

Background shapes important.

R(W/Z) : New Approach

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Acceptance : made similar for W's & Z's :

PDF Uncertainty :

Parameterize above acceptance functions :

Reweight large event ensembles to correspond to error PDF sets.

R(W/Z) : PDF Uncertainty

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Zmm (new)

Wmn (new)

Zmm (old)

Wmn (old)

R (old)

R (new)

CTEQ 6.1

R(W/Z) : PDF Uncertainty

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W

Z

Future measurements (d/dy ?) might constrain relevant PDF sets ?

Even without further constraints, PDF systematic on R  0.5%

R(W/Z) : Prospects

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Correlations between charges/legs have been studied : minimal.

With 400-500 pb-1 : new method should have a similar statistical precision to the current (72 pb-1) determination of R, with considerably smaller systematics.

W Charge Asymmetry

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Rapidity charge asymmetry is sensitive to d(x)/u(x) ratio at high-x  primary interest of PDF fitters.

cannot reconstruct yW directly

measure charged lepton only



W Charge Asymmetry

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Systematics :

Charge mis-identification : dominant

Backgrounds.

Calorimeter energy scales, etc.

calorimeter seeded silicon tracking

COT (central drift chamber) tracking

Look for evidence of charge dependent charge mis-id rate :

C. Issever, A. Scott, D. Stuart (UCSB); T. Nelson (FNAL)

PRD71, 051104 (2005)

W Charge Asymmetry

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Decay asymmetry enhanced.

e  yW as ET

Production asymmetry enhanced.

Different x region probed.

W Charge Asymmetry

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Comparison with error PDF's

W Charge Asymmetry : New Approach

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B. Han, A. Bodek, Y. Chung, E. Halkiadakis, K. McFarland (U.Rochester)

Next logical step : exploit kinematic value of events to their full.

Attempt to reconstruct yW and measure production asymmetry directly.

W Charge Asymmetry : New Approach

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Unknown pZ(n) : reconstruct two solutions y1, y2 :

q(p) / q(p) production ratio (from MC)

Weight each solution by (y) and iterate for the asymmetry :

W Charge Asymmetry : New Approach

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Preliminary sensitivity study :

Production charge asymmetry can be directly measured.

Statistical precision improved over lepton asymmetry measurement.

No known large additional systematics due to the method (charge mis-id will likely dominate).

[ Correlations present in new method : quantitative analysis of PDF sensitivity in progress ]

[ ET(e) > 25 GeV; missing-ET > 25 GeV; standard ID cuts; 400pb-1 ]

W Charge Asymmetry : New Approach

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Example :

Dependence of q / q ratio on PDF's.

 0.5% (compared to few % charge mis-id)

400 pb-1 measurement should significantly constrain PDF's.

Other W/Z Measurements

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Cross sections :

s(We) using forward electrons.

Tau's :

s(W) and s(W)/s(We)

s(Z/*(l)(h))

Differential cross-section measurements :

ds(Z/*l+l-)/dpT

ds(Z/*l+l-)/dy

d2s(Z/*l+l-)/dpTdy (?)

AFB(Z) : neutral current couplings; Z' searches. Second generation analyses under way (new methods).

Diboson measurements :

Complete set of cross-section measurements (W, Z, WW) or limits (WZ,ZZ) using leptonic decay channels.

Anomalous coupling limits from W, Z, WWll, WW/WZljj

Starting work on more challenging channels : WZlbb, ZZ/ZWl+l-jj

Conclusions

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First round of inclusive cross-section measurements mostly complete.

Now focusing on optimising analysis methods for the most interesting physics :

R  width

Asymmetry  PDF's

t/e  universality

Some smart ideas !

PDF and other production uncertainties can eventually limit precision measurements such as MW. Still need to understand quantitatively how Tevatron measurements themselves (asymmetries, ds/dpT, etc. ) can reduce such uncertainties.

David Simon

2005-04-18T21:52:06

David Simon