boson gauge couplings at lep

March 8 2005March 8 2005Paolo SPAGNOLO – INFN PIPaolo SPAGNOLO – INFN PI

Boson Gauge Couplings at LEPBoson Gauge Couplings at LEP

Paolo SPAGNOLOPaolo SPAGNOLOINFN PisaINFN Pisa

For the Four LEP Collaborations ADLOFor the Four LEP Collaborations ADLO

40th Rencontres De Moriond On Electroweak Interactions And Unified 40th Rencontres De Moriond On Electroweak Interactions And Unified TheoriesTheories

8 Mar 2005, La Thuile, Aosta Valley, Italy8 Mar 2005, La Thuile, Aosta Valley, Italy


LEP collider performanceLEP collider performance

LEP: eLEP: e++ee-- collider at CERN collider at CERN LEP1: ELEP1: ECMCM ~ M ~ MZZ from 1989 to 1995 from 1989 to 1995 LEP2: ~ 700 pbLEP2: ~ 700 pb-1-1 /exp above WW production threshold from 1996 to 2000 /exp above WW production threshold from 1996 to 2000

183 GeV

189 GeV

192-202 GeV

202-208 GeV

161-172 GeV


Results from the LEP experimentsResults from the LEP experiments

Main analyses (cross section, W mass, TGC) by all Main analyses (cross section, W mass, TGC) by all experimentsexperiments– Results combined by joint LEP Working GroupsResults combined by joint LEP Working Groups– Common systematics and correlationsCommon systematics and correlations– Almost all the statistics analyzedAlmost all the statistics analyzed– A lot of results still preliminary, many final publications this A lot of results still preliminary, many final publications this

year !!year !!ALEPHALEPH DELPHIDELPHI L3L3 OPALOPAL

20032003 20042004 20022002 20032003

ffff 20052005 20052005 20052005 20042004

ZZZZ 20052005 20032003 20032003 20042004

W+W-W+W- 20042004 20042004 20042004 20052005

TGCTGC 20052005 20052005 20042004 20042004

ZZ 20052005 20052005 20042004 20042004

mmWW 20052005 20052005 20052005 20052005


Physics processes at LEP2Physics processes at LEP2

~100k evts

~10k evts

~1k evts

~100 evts


Boson Gauge CouplingsBoson Gauge Couplings

Standard Model :Standard Model : non-Abelian SU(2)xU(1) gauge symmetry non-Abelian SU(2)xU(1) gauge symmetry– cTGCcTGC charged triple Gauge Couplings: charged triple Gauge Couplings: WWWW, WWZ, WWZ– cQGCcQGC charged quartic Gauge Couplings: charged quartic Gauge Couplings: WWWW, WWZ, WWZ, WWZZ, WWWW, WWZZ, WWWW (small or negligible at LEP)(small or negligible at LEP)

Search for Search for anomalous Gauge Couplingsanomalous Gauge Couplings– charged: beyond the SMcharged: beyond the SM– neutral: not in the SM: neutral: not in the SM: nTGC: ZZZ, ZZnTGC: ZZZ, ZZ, Z, Zand nQGC: ZZand nQGC: ZZ

Gauge bosons production requiredGauge bosons production required

LEP2 energy allowed these studies for the “first time”LEP2 energy allowed these studies for the “first time”


Charged Triple Gauge CouplingsCharged Triple Gauge Couplings

Sensitivity to TGCs in 3 processesSensitivity to TGCs in 3 processes– WW pairs productionWW pairs production– single W productionsingle W production– single photon productionsingle photon production


W-pair eventW-pair eventss

qqqq

qq,Weqq,Weqqqq

qq, Zeeqq, Zee

,,, ll, llbkgbkg

75-80%75-80%80-90%80-90%qqqqqqqq 45% 45%

80-85%80-85%50-80%50-80%qqqq 15%15%

~95%~95%75-90%75-90%qqqq 15%15%

~90%~90%75-90%75-90%eeqqqq 15%15%

80-90%80-90%50-80%50-80%llll 11%11%

puritypurityefficiencyefficiencyChannelChannel

WWee WW eqq (~15%)

Gauge Couplings !


WW qqqq (~45%) WW qq (~15%)


WW qq (~15%) WW e(~4%)


Backgrounds in WW cross sectionBackgrounds in WW cross section

All 4f diagrams (eqq)

Andrea Venturi

Devo mettere altro ??quanto grande correzione 4f-cc03 ?


LEP combinationLEP combination WWWW from each exp combined from each exp combined

– Precision better than 1%Precision better than 1%

– systematics correlation matrixsystematics correlation matrix

– test the SM radiative correction to test the SM radiative correction to CC03 diagramsCC03 diagrams


W-pair cross sectionsW-pair cross sections

exchange t channel ONLY



exchange and WW vertex



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


Single W….Single W….

In agreement with SM within 8% precision

Weee

W

Sensitive to the WWZ

and WW couplings


… … and single Zand single Z

In agreement with SM within 7% precision

Zeeee


Single Single

08.084.2 N

ee

Sensitive to the WW couplings outside Z resonance !!


TripleTriple Gauge Couplings Gauge Couplings

Standard electroweak theory

U(1)

SU(2)

triple and quartic SU(2) gauge boson self couplings are the signature of the non-Abelian SU(2) electroweak

structure !

The most general Lorentz Invariant WWV (V= + Z) vertex has 7+7 = 14 complex couplings

VV

VV

VVV

~~gg

g

54

1

magnetic dipole moment (1 )2W

W

e

M

electric dipole moment ( )2W

W

ed

M

1electric charge WQ eg


TripleTriple Gauge Couplings Gauge Couplings

C and P conservation only 6 real out of 14 complex parameters

SU(2)L⊗U(1)Y only 3 free parameters


W

*l

*l

l

W

W

q

q '

e e

*q

*q

Most important process for studying TGCs is e e W W

W

*l*l

W Polar angle

fermion polar angle wrt the W direction

fermion azimuthal angle wrt the WW plane

*f

WW

W

WW

d

d

d

d

The WWZ and WW gauge couplings can be measured in W-

pair events, fitting the W-pair event rates and the W production

and decay angular distributions.


Use angular distributions from all event topologies:

W W l qq

qqqq

l l

Do W charge tagging to obtain direction in events W qqqq

Use Monte Carlo to correct for detector effects and to implement radiative corrections

Triple Gauge Couplings: AnalysisTriple Gauge Couplings: AnalysisW W


Triple Gauge Couplings: 1d & 2d Fit Triple Gauge Couplings: 1d & 2d Fit LEP ResultsLEP Results

3 parameters fit with C and P cons. and SU(2)L⊗U(1)Y


Triple Gauge Couplings: 3d Fit ResultsTriple Gauge Couplings: 3d Fit Results

3 parameters fit with C and P cons. and SU(2)L⊗U(1)Y


Triple Gauge CouplingsTriple Gauge Couplings

Relaxing all constraints and fitting for any of the 28WWZ and WW couplings

one-dimensional fit resultsfor the SM non-zero TGC values

(ALEPH data only)

… all other 24 couplings are consistent with zero (within 5-20%) !

Proof of the Standard Model SU(2)L⊗U(1)Y

Structure

0.0611.065Re

0.0621.071Re

0.0731.066gRe

0.0911.123gRe

Z

Z1

1


Neutral TGC (excluded by SM)Neutral TGC (excluded by SM)

Investigated in ZZ and ZInvestigated in ZZ and Z processes processes ZZ on shell: 4 parameters fZZ on shell: 4 parameters f44

ZZ, f, f44, f, f55

ZZ, f, f55

ZZ on shell: 8 parameters h on shell: 8 parameters hiiZZ, h, hii

(i=1,4) (i=1,4) Z angular distribin bosted frame

ZZ

Andrea Venturi

precisione R per ZZ


nTGC combined resultsnTGC combined results


Quartic Gauge CouplingsQuartic Gauge Couplings QGC at LEP: WWQGC at LEP: WW, WWZ, WWZ, ZZ, ZZ

– 5 parameters: a5 parameters: aWW00, a, aWW

cc, a, aWWnn, a, aZZ

00, a, aZZcc

Total cross sectionTotal cross section Photon energy and angular distributionPhoton energy and angular distribution

OPAL

SM forbidden


DELPHI OPALL3

20

2

2

0.020 / 0.020

0.053 / 0.037

0.160 / 0.150c

n

a

a

a

95% C.L. Limits on quartic couplings in from2GeV

20

2

2

0.017 / 0.017

0.052 / 0.026

0.140 / 0.130c

n

a

a

a

20

2

2

0.020 / 0.020

0.063 / 0.032

0.180 / 0.140c

n

a

a

a

W W

95% C.L. Limits on quartic couplings in from ZZ 2GeV


CONCLUSIONSCONCLUSIONS

The Standard ModelThe Standard Model non-Abelian non-Abelian SU(2)xU(1)SU(2)xU(1) gauge symmetry gauge symmetry PROVED!!!PROVED!!!

– MEASURED cTGCsMEASURED cTGCs charged triple Gauge Couplings: charged triple Gauge Couplings: WWWW, WWZ , WWZ – NEGLIGIBLE cQGCNEGLIGIBLE cQGC quartic Gauge Couplings: quartic Gauge Couplings: WWWW, WWZ, WWZ, WWZZ, , WWZZ,

WWWWWWWW

EXCLUDED EXCLUDED anomalous Gauge Couplingsanomalous Gauge Couplings– charged: beyond the SMcharged: beyond the SM– neutral: not in the SM: neutral: not in the SM: nTGC: ZZZ, ZZnTGC: ZZZ, ZZ, Z, Zand nQGC: ZZand nQGC: ZZ

one of the most important results of LEP2one of the most important results of LEP2


W Polarization in

W

W

Measure spin density matrices and extract polarized diff cross sec

Fit for (L3) Use avg value of projection op (OPAL)

W( ,cos )kk s

kk kk

e e W W

190GeVs


Form Factor for Vector Resonance Enhancement of L Le e W W

Re( )TF

Map triangle onto plane ( , / )M M

For the technirho mass at 95% C.L. 1M

675M GeV

For the technirho mass at 95% C.L. 0.5M

775M GeV

12

2

12

2 2 21 11T

s

M M M

s

M MF i

TF

Im( )TF

Triangle correponds to 95%CL allowed region with

Re( ) , Im( ) 0T TF F

95%CL contour w/ center = (.96,-.15)

ALEPH Preliminary


W Boson Production at LEP2W Boson Production at LEP2

ee++ee W W++WW ee++ee We Weee

,Z

,Z


Event selection: qqqqEvent selection: qqqq Event propertiesEvent properties

– Large multiplicityLarge multiplicity– no missing momentumno missing momentum– 4jet-like4jet-like

Main background: qq(g)Main background: qq(g) Multidimensional techniques Multidimensional techniques

(NN, pdf, ...)(NN, pdf, ...)

Eff. ~ 90%, purity ~ 85 %Eff. ~ 90%, purity ~ 85 %

Main systematics ~1.3 Main systematics ~1.3 ÷÷ 2.%: 2.%:– hadronization models (signal and hadronization models (signal and

bkg)bkg) correlated among experiments !!correlated among experiments !!

– detector simulationdetector simulation

Andrea Venturi

controllare i sistematiciscrivere valore sistematico %


Event selection: lEvent selection: lqqqq Two jets + high energy and Two jets + high energy and

isolated lepton (or isolated lepton (or jet) + jet) + missing pmissing ptt

Main backgrounds: qq(Main backgrounds: qq() and ) and 4f (non-WW)4f (non-WW)

Multivariable selectionsMultivariable selections Eff. 60-90%, purity ~ 80-95%Eff. 60-90%, purity ~ 80-95%

Main systematics ~1.4 Main systematics ~1.4 ÷÷ 2.5%:2.5%:– lepton-idlepton-id

– background subtractionbackground subtraction

Andrea Venturi

verificare sistematiciverificare efficienze e bkgvalore syst %


Event selection: lEvent selection: lll Low multiplicityLow multiplicity

– two leptons or thin jets (two leptons or thin jets ( jets) jets)

Missing pMissing ptt and acoplanarity and acoplanarity

– cuts depend on lepton flavourcuts depend on lepton flavour

Main background: Main background: – two photons ,di-leptons, 4f non-two photons ,di-leptons, 4f non-

WWWW

Eff. ~50-80%, purity ~80-90%Eff. ~50-80%, purity ~80-90%

Main systematics ~1.3-Main systematics ~1.3-4.5%:4.5%:– background subtractionbackground subtraction

– lepton identificationlepton identification

– beam related detector beam related detector noisenoise

Andrea Venturi

verificare sistematiciverificare eff e bkgvalore syst %


O(O() radiative correction to WW production) radiative correction to WW production

Not available at the beginning of LEP2Not available at the beginning of LEP2

No correction:~2% highercross section.No effect on acceptance

TGC: ~1% change in WW production angle

W mass: peak distortionsand radiation:compensation: < 5-10 MeV

boson gauge couplings at lep

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ww gauge couplings

quartic gauge couplings

analysistriple gauge

triple gauge couplingsthe

w mass

w charge

wwg couplings

wpair event rates