Trilinear Gauge Boson Couplings Research Articles

Measurement of the Zγ→νν‾γ production cross section in pp collisions at s=8 TeV and limits on anomalous ZZγ and Zγγ trilinear gauge boson couplings

A measurement of the Z gamma to nu nu-bar gamma production cross section in pp collisions at sqrt(s) = 8 TeV is presented, using data corresponding to an integrated luminosity of 19.6 inverse femtobarns collected with the CMS detector at the LHC. This measurement is based on the observation of events with large missing energy and with a single photon with transverse momentum above 145 GeV and absolute pseudorapidity in the range |eta| < 1.44. The measured Z gamma to nu nu-bar gamma production cross section, 52.7 +/- 2.1(stat) +/- 6.4 (syst) +/- 1.4 (lumi) fb, agrees well with the standard model prediction of 50.0 +2.4 -2.2 fb. A study of the photon transverse momentum spectrum yields the most stringent limits to date on the anomalous Z-Z-gamma and Z-gamma-gamma trilinear gauge boson couplings.

Trilinear gauge boson couplings in the gauge—Higgs unification

We examine trilinear gauge boson couplings (TGCs) in the context of the SU (3)W ⊗ U (1) � gauge–Higgs unification scenario. The TGCs play important roles in probes of the physics beyond the standard model, since they are highly restricted by the experiments. We discuss the mass spectrum of the neutral gauge boson with brane-localized mass terms carefully and find that the TGCs and ρ parameter may deviate from standard model predictions. Finally, we put a constraint on these observables and discuss the possible parameter space.

Trilinear gauge boson couplings in the standard model with one universal extra dimension

One-loop effects of Standard Model (SM) extensions comprising universal extra dimensions are essential as a consequence of Kaluza-Klein (KK) parity conservation, for they represent the very first presumable virtual effects on low-energy observables. In this paper, we calculate the one-loop $CP$-even contributions to the SM $WW\ensuremath{\gamma}$ and $WWZ$ gauge couplings produced by the KK excited modes that stand for the dynamical variables of the effective theory emerged from a generalization of the SM to five dimensions, in which the extra dimension is assumed to be universal, after compactification. The employment of a covariant gauge-fixing procedure that removes gauge invariance associated to gauge KK excited modes, while keeping electroweak gauge symmetry manifest, is a main feature of this calculation, which is performed in the Feynman-'t Hooft gauge and yields finite results that consistently decouple for a large compactification scale. After numerical evaluation, our results are comparable with the one-loop SM contributions and well within the reach of a next linear collider.

A Bayesian view of the Higgs sector with higher dimensional operators

Abstract We investigate the possibilities of New Physics affecting the Standard Model (SM) Higgs sector. An effective Lagrangian with dimension-six operators is used to capture the effect of New Physics. We carry out a global Bayesian inference analysis, considering the recent LHC data set including all available correlations, as well as results from Tevatron. Trilinear gauge boson couplings and electroweak precision observables are also taken into account. The case of weak bosons tensorial couplings is closely examined and NLO QCD corrections are taken into account in the deviations we predict. We consider two scenarios, one where the coefficients of all the dimension-six operators are essentially unconstrained, and one where a certain subset is loop suppressed. In both scenarios, we find that large deviations from some of the SM Higgs couplings can still be present, assuming New Physics arising at 3 TeV. In particular, we find that a significantly reduced coupling of the Higgs to the top quark is possible and slightly favored by searches on Higgs production in association with top quark pairs. The total width of the Higgs boson is only weakly constrained and can vary between 0.7 and 2.7 times the Standard Model value within 95% Bayesian credible interval (BCI). We also observe sizeable effects induced by New Physics contributions to tensorial couplings. In particular, the Higgs boson decay width into Zγ can be enhanced by up to a factor 12 within 95% BCI.

Limits on anomalous trilinear gauge boson couplings from WW, WZ and Wγ production in [formula omitted] collisions at [formula omitted

We present searches for the anomalous γWW and ZWW trilinear gauge boson couplings from WW and WZ production using lepton plus dijet final states and a combination with results from Wγ, WW, and WZ production with leptonic final states. The analyzed data correspond to up to 8.6 fb−1 of integrated luminosity collected by the D0 detector in pp¯ collisions at s=1.96 TeV. We set the most stringent limits at a hadron collider to date assuming two different relations between the anomalous coupling parameters Δκγ, λ, and Δg1Z for a cutoff energy scale Λ=2 TeV. The combined 68% C.L. limits are −0.057<Δκγ<0.154, −0.015<λ<0.028, and −0.008<Δg1Z<0.054 for the LEP parameterization, and −0.007<Δκ<0.081 and −0.017<λ<0.028 for the equal couplings parameterization. We also present the most stringent limits of the W boson magnetic dipole and electric quadrupole moments.

Measurements of CP-conserving trilinear gauge boson couplings WWV (V≡γ,Z) in e+e− collisions at LEP2

The data taken by DELPHI at centre-of-mass energies between 189 and 209 GeV are used to place limits on the CP-conserving trilinear gauge boson couplings Delta_g1z, lambda_gamma and Delta_kappag associated to W+W- and single W production at LEP2. Using data from the jjlv, jjjj, jjX and lX final states, where j, l and X represent a jet, a lepton and missing four-momentum, respectively, the following limits are set on the couplings when one parameter is allowed to vary and the others are set to their Standard Model values of zero: Delta_g1z = -0.025^{+0.033}_{-0.030}, lambda_gamma = 0.002^{+0.035}_{-0.035} and Delta_kappag = 0.024^{+0.077}_{-0.081} . Results are also presented when two or three parameters are allowed to vary. All observations are consistent with the predictions of the Standard Model and supersede the previous results on these gauge coupling parameters published by DELPHI.

Measurement of trilinear gauge boson couplings fromWW+WZ→lνjjevents inpp¯collisions ats=1.96 TeV

We present a direct measurement of trilinear gauge boson couplings at gammaWW and ZWW vertices in WW and WZ events produced in pp-bar collisions at sqrt{s}=1.96 TeV. We consider events with one electron or muon, missing transverse energy, and at least two jets. The data were collected using the D0 detector and correspond to 1.1/fb of integrated luminosity. Considering two different relations between the couplings at the gammaWW and ZWW vertices, we measure these couplings at 68% C.L. to be kappa_{gamma}=1.07^{+0.26}_{-0.29}, lambda =0.00^{+0.06}_{-0.06} and g_{1}^{Z}=1.04^{+0.09}_{-0.09} in a scenario respecting SU(2)_L x U(1)_Y gauge symmetry and kappa =1.04^{+0.11}_{-0.11} and lambda=0.00^{+0.06}_{-0.06} in an "equal couplings" scenario.

Diboson production at D0

New data set recorded by Dø experiment at the Tevatron collider at s√ = 1.96 TeV makes the diboson physics program an attractive probe of electroweak gauge structure in the Standard Model. Here we present the most recent diboson production cross section measurements at Dø for Wγ, Zγ, WZ and ZZ and report on the tightest limits to date on the neutral trilinear gauge boson couplings in Zγ production. Depending on the analysis the size of utilized RunIIa data collected during 2002-2006 by the Dø detector is 0.8-1.0 pb-1.

Anomalies, anomalous U(1)'s and generalized Chern-Simons terms

A detailed analysis of anomalous U(1)'s and their effective couplings is performed both in field theory and string theory. It is motivated by the possible relevance of such couplings in particle physics, as well as a potential signal distinguishing string theory from other UV options. The most general anomaly related effective action is analyzed and parameterized. It contains Stuckelberg, axionic and Chern-Simons-like couplings. It is shown that such couplings are generically non-trivial in orientifold string vacua and are not in general fixed by anomalies. A similar analysis in quantum field theories provides similar couplings. The trilinear gauge boson couplings are also calculated and their phenomenological relevance is advocated. We do not find qualitative differences between string and field theory in this sector.

CHARGED TGC FROM 1999 DELPHI DATA

Measurements of the trilinear gauge boson couplings WWγ and WWZ are presented from data taken by DELPHI in 1999 at an energy ranging from 192 to 202 GeV. Values are extracted with respect to [Formula: see text] and Δ κγ, the differences of the WWZ charge coupling and of the WWγ dipole coupling from their Standard Model values, and λγ, the WWγ quadrupole coupling. The study uses data from the final states jjℓν, jjjj, ℓX, jjX and γX, where j represents a quark jet, l an identified lepton and X missing four-momentum. The observations are consistent with the Standard Model predictions.

Trilinear gauge boson couplings and bilepton production in the SU(3)C⊗SU(3)L⊗U(1)N models

The trilinear gauge boson couplings in the SU(3)C⊗SU(3)L⊗U(1)N (3-3-1)models are presented. We find that new Z2 does not interact with the usual (in the standard model) gauge bosons Z,W±. Based on these results, production of new heavy gauge bosons at high energy colliders such as e+e− is calculated. We show that the cross sections obtained in the 3-3-1 model with right-handed neutrinos can be one order bigger than the same in the minimal 3-3-1 model.

Measurement of trilinear gauge boson couplings WWV, ( V≡ Z, γ) in e+e− collisions at 189 GeV

Measurements of the trilinear gauge boson couplings WWγ and WWZ are presented using the data taken by DELPHI in 1998 at a centre-of-mass energy of 189 GeV and combined with DELPHI data at 183 GeV. Values are determined for Δg 1 Z and Δκ γ , the differences of the WWZ charge coupling and of the WWγ dipole coupling from their Standard Model values, and for λ γ , the WWγ quadrupole coupling. A measurement of the magnetic dipole and electric quadrupole moment of the W is extracted from the results for Δκ γ and λ γ . The study uses data from the final states jjℓ ν, jjjj, ℓ X, jjX and γX, where j represents a quark jet, ℓ an identified lepton and X missing four-momentum. The observations are consistent with the predictions of the Standard Model.

PHYSICS OF W BOSONS AT LEP2

After the first observations of W bosons in leptonic interactions, about 4000 WW candidate events per experiment have been collected at LEP2. This data allows the measurement of the WW production cross section at different center-of-mass energies, as well as W decay branching fractions. The W hadronic branching fraction can be converted into a test of the unitarity of the CKM matrix, or into an indirect determination of the matrix element |V cs |. A more direct measurement coming from charm tagging is also performed. The W mass has been measured via the cross section (in the threshold region) and the direct reconstruction of the W decay products, using different techniques to account for the distortions due to experimental effects. The main systematic error to the mass reconstruction in the fully hadronic channel comes from QCD effects like Color reconnections and Bose–Einstein correlations, extensively studied in WW events. In e+e- collisions W pairs can be produced in s-channel via a three-vector boson vertex, so a direct study of the trilinear gauge boson couplings is possible. Modification of WW cross section and distributions of W production and decay angles would be an indication of nonstandard couplings, thus a first hint for the presence of new physics.

Measurements of the trilinear gauge boson couplings WWV (V≡γ,Z) in e+e− collisions at 183 GeV

Measurements of the trilinear gauge boson couplings WWγ and WWZ are presented from data taken by DELPHI in 1997 at an energy of 183 GeV. From a study of the reactions e+e−→W+W−, e+e−→Weν and e+e−→ννγ, values are obtained for Δg1Z and Δκγ, the differences of the WWZ charge coupling and of the WWγ dipole couplings from their Standard Model values, and for λγ, the WWγ quadrupole coupling. The observations are consistent with the predictions of the Standard Model.

W physics at LEP

After the first observations of W bosons in leptonic interactions, about 1000 WW candidate events per experiment have been collected at LEP2. This allows the measurement of the WW production cross section at different centre-of-mass energies, as well as W decay branching fractions. The W hadronic branching fraction can be converted into a test of the unitarity of the CKM matrix, or into an indirect determination of the matrix element | V cs |. A more direct measurement comes from a charm tag performed on jets from W decays. The W mass has been measured via the cross section (in the threshold region) and the direct reconstruction of the W decay products, using different techniques to account for the distortions due to experimental effects. The cross sections, together with distributions of W production and decay angles, are used to measure trilinear gauge boson couplings.

Trilinear gauge couplings at the Fermilab Tevatron

Recent trilinear gauge boson couplings measurements by the CDF and DØ Collaborations at the Fermilab Tevatron are presented. The measurements were done by analyzing diboson production in multiple decay channels and final states. No deviations from the Standard Model description of the WWZ, WWγ, ZZγ and Zγγ vertices were found. Limits on anomalous gauge couplings set by these analyses are the tightest available to date.

Electroweak results from hadron colliders

A review of recent electroweak results from hadron colliders is given. Properties of the W ± and Z 0 gauge bosons using final states containing electrons and muons based on large integrated luminosities are presented. The emphasis is placed on the measurement of the mass of the W boson and the measurement of trilinear gauge boson couplings.

Measurement of trilinear gauge couplings in e+e− collisions at 161 GeV and 172 GeV

Trilinear gauge boson couplings are measured using data taken by DELPHI at 161 GeV and 172 GeV. Values for WWV couplings ( V = Z , γ ) are determined from a study of the reactions e + e − → W + W − and e + e − → Weν , using differential distributions from the WW final state in which one W decays hadronically and the other leptonically, and total cross-section data from other channels. Limits are also derived on neutral ZVγ couplings from an analysis of the reaction e + e − → γ + invisible particles .

Measurement of the WWγ and WWZ couplings at LEP200: the benefits of higher energy?

We performed a detailed analysis of the process e +e − → ℓνq q′ to determine its sensitivity to anomalous trilinear gauge boson couplings of the WWγ and WWZ vertices and how the sensitivity varies with energy and integrated luminosity. We included all tree level Feynman diagrams that contribute to this final state and used a maximum likelihood analysis of a five dimensional differential cross-section based on the W and W decay product angular distributions. For constant luminosity, increasing s from 175 GeV to 192 GeV (220 GeV) improves the measurement sensitivity by a factor of 1.5–2 (2–3) depending on the parameter measured. However, the lower luminosity expectd at higher s will reduce these improvements. In any case, the sensitivities for s =175 and L = 500 pb −1 of δg 1 z = ±0.22, δκ z = ±0.20, δκ γ = ±0.27, δL 9 l = ±5, and δL 9r = −230 +330 are likely to be at least an order of magnitude too big to see the effects of new physics.

W-pair production in the process e+e--->l nu qq-bar' and measurement of the WW gamma and WWZ couplings.

We performed a detailed analysis of the process $e^+e^-\to \ell \nu q\bar{q}'$ where we included all tree level Feynman diagrams that contribute to this final state. We studied the sensitivity of this process to anomalous trilinear gauge boson couplings of the $WW\gamma$ and $WWZ$ vertices using two popular parametrizations. We used a maximum likelihood analysis of a five dimensional differential cross-section based on the $W$ and $W$ decay product angular distributions. We concentrated on LEP-200 energies, taking $\sqrt{s}=175$ GeV, and energies appropriate to the proposed Next Linear Collider (NLC), a high energy $e^+e^-$ collider with center of mass energies $\sqrt{s}=500$ and 1~TeV. At 175 GeV, $g_1^Z$ can be measured to about $\pm 0.2$, $\kappa_Z$ to $\pm 0.2$ and $\kappa_\gamma$ to $\pm 0.3$, $\lambda_Z$ to $\pm 0.2$ and $\lambda_\gamma$ to $\pm 0.3$. at 95\% C.L. assuming 500~pb$^{-1}$ integrated luminosity. Although these will be improvements of existing measurements they are not sufficiently precise to test the standard model at the loop level and are unlikely to see deviations from SM expectations. At 500~GeV with 50~fb$^{-1}$ integrated luminosity, $g_1^Z$ can be measured to about $\pm 0.01$, $\kappa_Z$ and $\kappa_\gamma$ to $\pm 0.005$ and $\lambda_Z$ and $\lambda_\gamma$ to $\pm 0.003$ at 95\% C.L. while at 1 TeV with 200~fb$^{-1}$ integrated luminosity, $\kappa_V$ and $\lambda_V$ can be measured to about $\pm 0.005$ and $\pm 10^{-3}$ respectively. The 500~GeV measurements will be at the level of loop contributions to the couplings and may show hints of new physics while the 1~TeV should be sensitive to new physics at the loop level.