The measurement of the triple gauge couplings in DELPHI

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Charged couplings from 183 GeV

Limits on anomalous WWV (V=Z,gamma) couplings are determined from a study of the reactions e+e- -> W+W-, e+e- -> Wev and e+e- -> nu nu gamma in the data collected by DELPHI at 183 GeV.
Different methods are used in the determination of the couplings from the different final states.

No deviation from the Standard Model expectations is found.
The table summarizes the values of the WWV couplings combining DELPHI data at 183 GeV from all the final states used in the analysis, and assuming the model of the couplings defined in 'Triple Gauge Couplings' in CERN 96-01, sec 2.1.1, p528.

Coupling parameter Fitted value 95% confidence interval
Delta g1(Z) 0.04 +/- 0.14 (stat) +/- 0.02 (syst) -0.21 < Delta g1(Z) < 0.32
Delta kappa_gamma 0.34 +0.26 -0.28 (stat) +/- 0.06 (syst) -0.19 < Delta kappa_gamma < 0.84
lambda_gamma -0.07 +0.19 -0.16 (stat) +/- 0.03 (syst) -0.36 < lambda_gamma < 0.31

The two ellipses show the 70% and 95% C.L. allowed regions in the plane of the two coupling parameters (lambda_gamma, Delta g1(Z)), with Delta kappa_gamma fixed at its Standard Model value, obtained from one of the analyses of the DELPHI data in the jjlv final state.





Details on the analyses can be found in DELPHI 98-94 CONF 162.




Charged couplings from 172 and 161 GeV

At the cms energy of 172 GeV, limits to the WWV coupling parameters were derived from the differential distributions from the WW final state in which one W decays leptonically and the other hadronically, and total cross-section data from other channels.
At 161 GeV, the number of W pairs measured by DELPHI was compared to the predicted number as a function of the anomalous coupling parameter alpha_WPhi. In addition, a limit for the CP-violating coupling parameter alpha_W(cp) has been obtained.

Combining these two energies DELPHI obtains
alpha_Wphi 0.22 +0.26 -0.28 (stat) +/- 0.06 (syst)
alpha_W 0.11 +0.48 -0.49 (stat) +/- 0.09 (syst)
alpha_Bphi 0.22 +0.66 -0.83 (stat) +/- 0.24 (syst)
alpha_BW(cp) 0.11 +0.71 -0.88 (stat) +/- 0.09 (syst)
alpha_W(cp) 0.19 +0.28 -0.41 (stat) +/- 0.11 (syst)
((cp) indicates the CP violating couplings)

The 172 GeV analysis is published in Phys.Lett.B423 (1998) 194 and you can get all the figures
. The extraction of limits from the 161 GeV data can be found in Phys.Lett. B397 (1997) 158.




Neutral couplings from 161, 172 and 183 GeV

Limits on anomalous Z-Z-gamma and Z-gamma-gamma couplings are extracted from the measured cross-section for e+e- -> nu nu gamma and e+e- -> q qbar gamma in the region of phase space where the photon has large energy and large polar angle.

The plot shows the predicted cross section for e+e- -> nu nu gamma as a function of the form factors h_3(Z) and h_3(gamma) for the anomalous couplings Z,Z,gamma and Z,gamma,gamma. A new physics scale lambda=1TeV has been assumed.

The horizontal lines show the cross-section measured by DELPHI with the data at 183 GeV.





The red ellipse shows the 95% C.L. allowed region for the form factors h_3(Z) and h_3(gamma) obtained from the DELPHI data. As a comparison the region allowed by unitarity is shown in green. A new physics scale Lambda=1TeV has been assumed.






The 183 GeV analyses can be found in DELPHI 98-93 CONF 161.
The single photon analysis was also performed on the data collected by DELPHI at 172 GeV. It is published in Phys.Lett.B423 (1998) 194 and you can get all the figures.

The combination with the other LEP experiments can be found here.