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
R. Brunelière Gauge Couplings at LEP2 2
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
R. Brunelière Gauge Couplings at LEP2 3
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
R. Brunelière Gauge Couplings at LEP2 4
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)
R. Brunelière Gauge Couplings at LEP2 5
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
R. Brunelière Gauge Couplings at LEP2 6
Cross-section
• Quadratic behaviour :
g = anomalous coupling
• Single W production useful for
ude e
11 Zg 1
221 ggSMTot
R. Brunelière Gauge Couplings at LEP2 7
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%)
R. Brunelière Gauge Couplings at LEP2 8
e+e Wee
qqee : Angle between the two jets, total transverse momemtum, NN output
llee: El, cos l, PT(lepton)
WW
ZZ
We
ALEPH
R. Brunelière Gauge Couplings at LEP2 9
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.
R. Brunelière Gauge Couplings at LEP2 10
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%)
R. Brunelière Gauge Couplings at LEP2 11
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
R. Brunelière Gauge Couplings at LEP2 12
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
R. Brunelière Gauge Couplings at LEP2 13
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
R. Brunelière Gauge Couplings at LEP2 14
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
R. Brunelière Gauge Couplings at LEP2 15
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
R. Brunelière Gauge Couplings at LEP2 16
Observables
• Cross-section
• Shape
– |cos()|, E , ,jet
– Optimal observables
G. Abbiendi et al., Eur. Phys. J. C17 (2000) 13.
R. Brunelière Gauge Couplings at LEP2 17
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
R. Brunelière Gauge Couplings at LEP2 18
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
R. Brunelière Gauge Couplings at LEP2 19
2D results
Correlation
79%
97%
Correlation
77%
76%
R. Brunelière Gauge Couplings at LEP2 20
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
R. Brunelière Gauge Couplings at LEP2 21
Coupling extraction
• Cross-section • Shape :– cos(Z)
– Optimal observables
14 f
14 Zf
15 f
15 Zf
OPAL PN482
DELPHI 2001-097
R. Brunelière Gauge Couplings at LEP2 22
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
R. Brunelière Gauge Couplings at LEP2 23
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.
R. Brunelière Gauge Couplings at LEP2 24
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
R. Brunelière Gauge Couplings at LEP2 25
• Signature : 2 acoplanar photons
• Photon definition (OPAL) :– E > 10 GeV
– |cos | < 0.9
• Coupling extraction : missing mass, E2
γγννee
OPAL PN510ALEPH 2003-009
R. Brunelière Gauge Couplings at LEP2 26
• 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)
R. Brunelière Gauge Couplings at LEP2 27
(2/2) γγqqee
• Shape :– E2 = energy of the least energetic photon
– max(|cos(1)|, |cos(2)|)
Phys. Lett. B540/1-2 (2002) 43
R. Brunelière Gauge Couplings at LEP2 28
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
R. Brunelière Gauge Couplings at LEP2 29
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
R. Brunelière Gauge Couplings at LEP2 30
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
R. Brunelière Gauge Couplings at LEP2 31
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
R. Brunelière Gauge Couplings at LEP2 32
2D results, ZZ channel
Correlation 2% -18%
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