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 Electroweak Physics
Dec 17, 2015
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,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)