r. brunelière gauge couplings at lep2 1 triple and quartic gauge couplings at lep 2 renaud...

R. Brunelière Gauge Couplings at LEP2 1

Triple and Quartic Gauge Couplings at LEP 2

Renaud BrunelièreLAPP - Université de Savoie

on behalf of the four LEP experiments


Outline

• Triple gauge boson couplings (TGC)– charged

W+W, W+WZ

– neutralZ, ZZ, ZZZ

• Quartic gauge boson couplings (QGC)W+W, W+WZ,ZZ,W+WZZ, W+WW+W

present in SM

not in SM


Gauge Boson Couplings

Why do we measure gauge boson couplings ?

• Test of the non-Abelian nature of the electroweak sector

• Probe for new physics at higher energies

How ?

Use an effective Lagrangian– modify existing SM couplings– introduce non-SM couplings

Anomalous couplings


Charged Triple Gauge Boson Couplings

• Generally

W+

W

W+

W

Z

7 parameters 7 parameters

V = Z,

• At LEP2

– C and P invariance

– U(1)Q

– SU(2)LU(1)Y

,,1Zg

V1g Vκ Vλ

V5gV4g Vκ~Vλ~

C +++ ++P +++ +

SM value1100000

K. Hagiwara et al.

Nucl.Phys. B282 (1987) 253-307

(at tree level)


Physics processes

• e+e W+W (CC03) • e+e Wee

and g1Z, and

188.6 GeV

=15.980.23 pb

188.6 GeV

=0.600.09 pb

• e+e ee


Cross-section

• Quadratic behaviour :

g = anomalous coupling

• Single W production useful for

ude e

11 Zg 1

221 ggSMTot


e+e W+W

Kinematic : 5 angles

OPAL PR381

lqq

most of the information in W

no flavor tagging W charge tagging in WW qqqq

channel (80%)


e+e Wee

qqee : Angle between the two jets, total transverse momemtum, NN output

llee: El, cos l, PT(lepton)

WW

ZZ

We

ALEPH


1D results

Existence of triple gauge couplings is proven.

Compatible with the Standard Model expectations.

Sensitive to radiative corrections (102)

SM

1

0

1

The other two couplings are set to their SM value

• New results from L3 including W+W qqqq & year 2000 for We.

• Update of results from ALEPH

• Final results from OPAL for WW pair production.


Systematics

Systematic sources correlated between experiments :

• e+e W+W

– Theory uncertainty on the cross-section (0.5%)– Theory uncertainty on angular distributions (YFSWW-RacoonWW)– Fragmentation – Color reconnection– Bose-Einstein correlations

• e+e Wee

– Theory uncertainty on the cross-section (5%)


2D results

The third coupling is set to its SM value.

029.0029.0γ

029.0029.01

036.0λ

024.1

Zg

048.0051.0γ

025.0021.0γ

026.1κ

024.0λ

049.0049.0γ

024.0025.01

984.0κ

004.1

Zg

ln(L) = 0.5


CP violating couplings

• Measurement of all CP-violating trilinear couplings separately.

• Analysis done with WW pairs (183 207 GeV) - ALEPH data only.

• For CP-conserving couplings, see

• Alternative approach : spin density method, see next talk.

Good agreement with SM

expectations

ALEPH 2003-035


Techni- form factor

Vector Resonance Enhancement of LLWWee2

2T

M i MF

M s i M

055.0966.0)Re(FT 097.0147.0)Im(FT

ALEPH data only

T.L.Barklow et al. “Strong Electroweak

Symmetry Breaking” hep-ph/9704217

( )M GeV

M

White region is excludedat 95% CL.

New

For , at 95% C.L. 0.5M

725M GeV


Neutral Triple Gauge Boson Couplings

At LEP2 : we assume final bosons are on-shell

Z*

Z*

*

Z*

Z*

Z*

*

Z*

*

15 CP-conserving forms + 29 CP-violating forms

We separate

e+e Z

*Z, Z* Ze+e ZZ

*ZZ, Z* ZZ

G.J.Gounaris, J.Layssac, F.M.Renard.

Phys.Rev. D62(2000) 073013

h couplings f couplings


e+e * Z, e+e Z* Z

• Anomalous couplings

• Standard model

CP - violatingγ2

γ1 hh

Z2

Z1 hh

CP - conservingγ4

γ3 hh

Z4

Z3 hh

Standard Model at tree level:

),(0 ZVhVi

Loop corrections :),(10 4 ZVhVi


Observables

• Cross-section

• Shape

– |cos()|, E , ,jet

– Optimal observables

G. Abbiendi et al., Eur. Phys. J. C17 (2000) 13.


1D results (1/2)

95% CLγ1h

055.0;056.0

γ2h

025.0;045.0

γ4h

034.0;002.0

γ3h

008.0;049.0

CP-violating

CP-conserving

*Z

• Update of results from L3


1D results (2/2)

95% CL

Z1h

13.0;13.0

Z2h

071.0;078.0

Z4h

034.0;002.0

Z3h

07.0;20.0

CP-violating

CP-conserving

Z*Z


2D results

Correlation

79%

97%

Correlation

77%

76%


e+e * ZZ, e+e Z* ZZ• Anomalous couplings

• Standard model

CP - violatingZ4

γ4 ff

CP - conservingZ

5γ

5 ff

Standard Model at tree level:

),(0 ZVf Vi

Loop corrections :),(10 4 ZVf Vi

188.6 GeV

=0.660.07 pb


Coupling extraction

• Cross-section • Shape :– cos(Z)

– Optimal observables

14 f

14 Zf

15 f

15 Zf

OPAL PN482

DELPHI 2001-097


1D results

95% CLγ4f

19.0;17.0

Z4f

30.0;30.0

Z5f

38.0;34.0

γ5f

36.0;32.0

CP-violating

CP-conserving• Final results from L3, OPAL

*ZZ Z*ZZ


Quartic Gauge Boson Couplings

W+

W

Z

Z

W+

W

Z

Wc

W aa0Zc

Z aa0 na

γγννee

γWW - ee

γWW - eeγγννee

γγqqee

G.Bélanger, F.Boudjema.

Phys.Lett. B288(1992) 201.

W.J.Stirling, A.Werthenbach.

Phys.Lett. C14(2000) 103.


Physics processes

• Anomalous couplings

• Main diagrams

• Coupling extraction

γWW - eeγγqqγγ,ννee

Cross-section + E , cos()

Cross-section + missing mass, E2, max(|cos(1)|, |cos(2)|)

Wc

W aa0Wc

W aa0Zc

Z aa0 na


• Signature : 2 acoplanar photons

• Photon definition (OPAL) :– E > 10 GeV

– |cos | < 0.9

• Coupling extraction : missing mass, E2

γγννee

OPAL PN510ALEPH 2003-009


• Cross-section

(1/2)γγqqee

Phys. Lett. B540/1-2 (2002) 43

• Signal definition :

For each photon E > 5 GeV |cos()|<0.97 (L3), |cos()|<0.95 (OPAL) cos(q)<0.98 (L3), cos(q)<0.90 (OPAL)

Invariant mass window |s’ mz| < 2Z (L3) 80 GeV < Mqq < 120 GeV (OPAL)


(2/2) γγqqee

• Shape :– E2 = energy of the least energetic photon

– max(|cos(1)|, |cos(2)|)

Phys. Lett. B540/1-2 (2002) 43


SM 22 16.0/ GeVanDELPHI 2003-059

γWW - ee• Cross-section • Shape

Signal = E>5 GeV, |cos |<0.95

cos f<0.90, |Mff’ MW| < 2W


WW, WWZ

2W0 /a

055.0;060.0

2Wc /a

093.0;099.0

2Wn /a

95% CL

• All results in GeV-2• New results from ALEPH for

• Final results from OPAL with WW

ALEPH

L3

OPAL

DELPHI

GeV 207γγνν

020.0;020.0 032.0;063.0 14.0;18.0 GeV 207WWγ

• No LEP combination

GeV 207γγνν GeV 207WWγ

015.0;015.0 026.0;048.0 13.0;14.0

GeV 207γγνν

GeV 207WWγ

052.0;054.0 14.0;15.0 020.0;020.0 037.0;053.0 15.0;16.0


ZZ

95% CL2Z

0 /a

021.0;008.0

2Zc /a

039.0;029.0

• All results in GeV-2 • New results from ALEPH for


Summary

Charged triple gauge boson couplings are measured (precision 10-2) using WW, single W productions

Neutral triple gauge boson couplings are studied with Z and ZZ events. Precision 10-2 - 10-1

Quartic gauge boson couplings are measured with WW, qq and events. Precision 10-2

In all these channels no significant deviations from Standard Model expectations are found.

Wait for current and next colliders : Tevatron, LHC, NLC


2D results, ZZ channel

Correlation 2% -18%

r. brunelière gauge couplings at lep2 1 triple and quartic gauge couplings at lep 2 renaud...

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