WW cross section and spin correlations at LEP

WW cross section and spin correlations at LEP

P.Azzurri SNS-PisaMoscow July 27 2006P.Azzurri SNS-Pisa

Moscow July 27 2006

XXXIII International Conference on High Energy Physics

Electroweak PhysicsElectroweak Physics

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 2

W pair productionW pair production

Tree level scattering unitarity electroweak renormalizability

SU(2)U(1) Gauge Cancellations

We

WW

WWZ

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 3

W pair events at LEPW pair events at LEP

qq

qq,Weqq

qq,Zee

,,ll

bkg

75-80%80-90%qqqq

80-85%50-80%qq

~95%75-90%qq~90%75-90%eqq

80-90%50-80%llpurityefficiencyChannel

W 1 3

W qq ' 2 3

WW (~ 10%)

WW qq ' (~ 45%)

WW qq 'qq ' (~ 45%)

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 4

Total cross sectionTotal cross section

4700 pb-1 at 161-209 GeV

mW 80.40 0.21 GeV/c 2

Clear proof of SU(2)xU(1)

gauge couplings !

Combination 2=26.6/24

Threshold mass

Hadronization uncertainty is largest common systematic (0.6% error)

OPAL final paper is coming

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 5

Data vs TheoryData vs Theory

Test of the SM radiative

corrections to the CC03 diagrams (~3%

effects)

Experimental precision

better than 1%

Theory uncertainty:• ~2%(161GeV) • 0.7%(170GeV) • 0.4%(200GeV)

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 6

cosW- distributioncosW- 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.

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 7

WW spin correlations WW spin correlations L3 - Eur.Phys.J.C40 (2005) 333

qql events only

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

cosW dependence of produced helicities select events with

0.9 cosW 0.3

0.3 cosW 0.9

backw: 26% (0,0)

forw: 69% (,)

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 8

WW spin correlations WW spin correlations

qql events

deplete/enhance hadr W helicity with cuts on |cosq*

|

Data CL to no spin correlations = 1%Data CL to KORALW SM = 35%

cosq 1 3

cosq 2 3

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 9

WW decay-plane correlations WW decay-plane correlations

From both qqqq & qql events

|| distribution corrected for

eff, bkg, wrong pairing

D 0.012 0.0210.012

KORALW

D 0.010 0.002

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 10

Spin density matrixSpin density matrixOPAL - Phys.Lett.B585 (2004) 223

L3 - Phys.Lett.B557 (2003) 147DELPHI - 2004-018 CONF 693

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

W-pair SDM

Direct limits on CP-violating TCG couplings

W longitudinal polarizationL=23.61.6% (SM 24%)

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 11

Z pairs productionsZ pairs productions

In agreement with SM within 5% precision

No gauge self couplings involved in Standard Model Z-pair production

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 12

Single W and Z eventsSingle W and Z events

In agreement with SM within 8% precisionIn agreement with SM within 7% precision

Zeeee Weee

Moscow 27/7/06 ICHEP06 P.Azzurri - WW cross sections and spin correlations at LEP 13

SummarySummary

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)

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)