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WW cross section and spin correlations at LEP. P.Azzurri SNS-Pisa Moscow July 27 2006. XXXIII International Conference on High Energy Physics Electroweak Physics. We . WW . WWZ. W pair production. SU(2) U(1) Gauge Cancellations.

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ww cross section and spin correlations at lep

WW cross section and spin correlations at LEP

P.Azzurri SNS-Pisa

Moscow July 27 2006

XXXIII International Conference on High Energy Physics

Electroweak Physics

w pair production

We

WW

WWZ

W pair production

SU(2)U(1) Gauge Cancellations

Tree level scattering unitarity  electroweak renormalizability

P.Azzurri - WW cross sections and spin correlations at LEP

w pair events at lep

Channel

efficiency

purity

bkg

ll

50-80%

80-90%

,,ll

eqq

75-90%

qq,Zee

~90%

qq

75-90%

~95%

qq

qq

50-80%

80-85%

qq,We

qqqq

80-90%

75-80%

qq

W pair events at LEP

P.Azzurri - WW cross sections and spin correlations at LEP

total cross section
Total cross section

4700 pb-1 at 161-209 GeV

OPAL final paper is coming

Clear proof of SU(2)xU(1) gauge couplings !

Combination 2=26.6/24

Hadronization uncertainty is largest common systematic (0.6% error)

Threshold mass

P.Azzurri - WW cross sections and spin correlations at LEP

data vs theory
Data vs Theory
  • Theory uncertainty:
  • ~2%(161GeV)
  • 0.7%(170GeV)
  • 0.4%(200GeV)

Experimental precision

better than 1%

Test of the SM radiative corrections to the CC03 diagrams (~3% effects)

P.Azzurri - WW cross sections and spin correlations at LEP

cos w distribution
cosW- distribution

Combined for possible future test of new theoretical models

qqe and qq channels only,

four energy bins

Identical 4f contributions reduced with additional cuts on the lepton direction (||>20), then subtracted.

P.Azzurri - WW cross sections and spin correlations at LEP

ww spin correlations
WW spin correlations

L3 - Eur.Phys.J.C40 (2005) 333

qql events only

cosW dependence of produced helicities select events with

forw: 69% (,)

backw: 26% (0,0)

Measure fractions f+,f-,f0 of W helicity states with the W rest frame lepton decay angle *

P.Azzurri - WW cross sections and spin correlations at LEP

ww spin correlations1
WW spin correlations

deplete/enhance hadr W helicity  with cuts on |cosq* |

qql events

Data CL to no spin correlations = 1%

Data CL to KORALW SM = 35%

P.Azzurri - WW cross sections and spin correlations at LEP

ww decay plane correlations
WW decay-plane correlations

From both qqqq & qql events

|| distribution corrected for eff, bkg, wrong pairing

P.Azzurri - WW cross sections and spin correlations at LEP

spin density matrix
Spin density matrix

OPAL - Phys.Lett.B585 (2004) 223

L3 - Phys.Lett.B557 (2003) 147

DELPHI - 2004-018 CONF 693

W-pair SDM

extract W helicities from angular distributions of decay products / fit to SDM elements

W longitudinal polarization

L=23.61.6% (SM 24%)

Direct limits on CP-violating TCG couplings

P.Azzurri - WW cross sections and spin correlations at LEP

z pairs productions
Z pairs productions

No gauge self couplings involved

in Standard Model Z-pair production

In agreement with SM within 5% precision

P.Azzurri - WW cross sections and spin correlations at LEP

single w and z events
Single W and Z events

In agreement with SM within 8% precision

In agreement with SM within 7% precision

P.Azzurri - WW cross sections and spin correlations at LEP

summary
Summary

1% accurate measurement of W-pair cross section has yielded the first direct and precision confirmation of the electroweak SU(2)U(1) structure

Nice measurements of W polarizations, spin and decay plane correlations, and spin density matrix (TGC related)

All LEP2 4f productions in good agreement (1-10%)

with the Standard Model prediction

Marginal changes expected for the final combination of results (very soon)

P.Azzurri - WW cross sections and spin correlations at LEP