Zγγ Couplings Research Articles

Probing anomalous ZZγ and Zγγ couplings at the e+e− colliders using optimal observable technique

We study the anomalous ZZγ and Zγγ couplings that can be probed via Zγ production at the e+e− colliders. We take Standard Model Effective Field Theory (SMEFT) approach to examine these anomalous neutral triple gauge couplings in a model independent way. There are four independent dimension-8 operators that generate these gauge interactions, one of them is CP-conserving and rest three are CP-violating. We adopt optimal observable technique to extract the sensitivity at which these anomalous couplings can be probed at future e+e− colliders and then compare the results with the latest experimental limit obtained at the LHC. We also study the impact and advantage of beam polarization in these precision measurements. Statistical limit (95% C.L.) on individual anomalous couplings as well as the correlation between various couplings have been discussed in detail.

Search for the anomalous ZZγ and Zγγ couplings via ννγ production at the CLIC

The non-Abelian gauge structure of the Standard Model implies the presence of the multi-boson self-interactions. Precise measurements in experimental and theoretical studies of these interactions allow not only testing the nature of the Standard Model but also new physics contribution coming from the beyond Standard Model. These interactions can be examined using a model-independent way in effective theory approach that composes the motivation part of this study. In this paper, we examine the anomalous ZZγ and Zγγ neutral triple gauge couplings via the process e−e+→Zγ for the neutrino-antineutrino pair decay of Z boson. It has performed with both unpolarized and polarized electron beams at the Compact Linear Collider with s=3 TeV. The study focused on CP-conserving CB˜W/Λ4 and CP-violating CBB/Λ4, CBW/Λ4, CWW/Λ4 couplings. Obtained sensitivities on the anomalous neutral triple gauge couplings with 95% Confidence Level are given with systematic uncertainties of 0%, 5% and 10% for unpolarized, −80% and 80% polarized electron beams with integrated luminosities of Lint=5ab−1, Lint=4ab−1 and Lint=1ab−1, respectively. Comparing the latest experimental limits and related phenomenological studies, our results on the anomalous neutral gauge couplings are set more stringent sensitivity between 10-30 times of magnitude.

$${\mathbf{Z}}(\nu \bar {\nu })\gamma $$Measurement and Neutral aTGC Limits at 13 TeV with the ATLAS Detector

The production of a Z boson in association with a high-energy photon (γ) in proton-proton collisions has been studied at the Large Hadron Collider (LHC). These studies have been used to test the electroweak sector of the Standard Model and to search for new physics effects, such as potential couplings of Z bosons to photons. The Zγ production with the Z boson decaying into neutrinos has been measured with data collected by the ATLAS detector during the 2015–2016 period at a center-of-mass energy of 13 TeV and corresponding to an integrated luminosity of 36.1 fb$^{–1}$. Candidate Zγ events with invisible decays of the Z boson are selected by requiring significant transverse momentum $({{p}_{T}})$ of the neutrinos system in conjunction with a single isolated photon with large transverse energy (E$_{T}$). Evidence of anomalous triple gauge-boson couplings is sought in Zγ production with photon E$_{T}$ greater than 600 GeV. No excess is observed relative to the Standard Model expectation, and upper limits are set on the strength of ZZγ and Zγγ couplings.

The projections on ZZγ and Zγγ couplings via [formula omitted] production in HL-LHC and HE-LHC

We investigate the sensitivity of the anomalous dimension-8 neutral triple gauge couplings via process pp→ννγ with fast detector simulation including pile-up effects for the post LHC experiments. The transverse momentum of the final state photon and missing energy transverse distributions are considered in the analysis. We obtain the sensitivity to the CB˜W/Λ4, CBB/Λ4, CWW/Λ4 and CBW/Λ4 couplings at HL-LHC and HE-LHC with an integrated luminosity of 3 ab−1 and 15 ab−1, respectively. Finally, our numerical results show that one can reach the constraints at 95% confidence level without systematic error on CB˜W/Λ4, CBB/Λ4, CWW/Λ4 and CBW/Λ4 couplings for HL-LHC (HE-LHC) as [−0.38;0.38]([−0.12;0.12]), [−0.21;0.21]([−0.085;0.085]), [−1.08;1.08]([−0.38;0.38]) and [−0.48;0.48]([−0.25;0.25]), respectively. They are better than the experimental limits obtained by LHC.

Measurement of the Zgamma to nu overline{nu}gamma production cross section in pp collisions at sqrt{s}=13 TeV with the ATLAS detector and limits on anomalous triple gauge-boson couplings

The production of Z bosons in association with a high-energy photon (Zγ production) is studied in the neutrino decay channel of the Z boson using pp collisions at sqrt{s}=13 TeV. The analysis uses a data sample with an integrated luminosity of 36.1fb−1 collected by the ATLAS detector at the LHC in 2015 and 2016. Candidate Zγ events with invisible decays of the Z boson are selected by requiring significant transverse momentum (pT) of the dineutrino system in conjunction with a single isolated photon with large transverse energy (ET). The rate of Zγ production is measured as a function of photon ET, dineutrino system pT and jet multiplicity. Evidence of anomalous triple gauge-boson couplings is sought in Zγ production with photon ET greater than 600 GeV. No excess is observed relative to the Standard Model expectation, and upper limits are set on the strength of ZZγ and Zγγ couplings.

Wγ AND Zγ PRODUCTION AND LIMITS ON ANOMALOUS WWγ, ZZγ AND Zγγ COUPLINGS WITH D0 DETECTOR

The recent D0 results on Wγ and Zγ production are presented. First, the cross-section and the difference in rapidities between photons and charged leptons for inclusive W(→lν)+γ production in eγ and μγ final states are discussed, then are the cross-section and differential cross-section as a function of photon transverse momentum for Zγ→l+l-(l = e, μ) process. Finally, I present the limits on anomalous WWγ, ZZγ and Zγγ couplings.

Possible anomalous ZZγ and Zγγ couplings and Z boson spin orientation in [formula omitted]: The role of transverse polarization

A formalism of a general spin-1 density matrix has been used to study the effect of the CP-conserving anomalous ZZγ and Zγγ couplings on the Z boson spin orientation in e + e − → Z γ with transversely polarized beams. Analytical expressions for the transverse polarization contributions from the Standard Model and from the interference of the Standard Model and anomalous couplings amplitudes to the Z boson polarization vector and the alignment tensor have been found. The main properties of these expressions have been presented and analyzed. It has been shown that the additional directions provided by the transverse polarization vectors of simultaneously polarized beams generate new measurables which can be used for disentangling different sets of couplings.

Top quark electric dipole and Zγγ couplings at a photon collider

Effect of the top quark electric dipole coupling and the Zγγ coupling is studied in the pair production of top quark at a photon collider using CP-violating asymmetries. Our results show that with a photon collider of geometrical luminosity of 20 fb −1 it is possible to put limits of the order of 0.1 on the Zγγ coupling and about 2.5×10 −17 e cm on the top quark electric dipole coupling using these asymmetries.

Study of theZZγandZγγCouplings inZ(νν)γProduction

We have measured the ZZγ and Zγγ couplings by studying 13.1pb -1 of pp→E t γ+X data at √s=1.8TeV with the DO detector at the Fermilab Tevatron Collider. This is the first study of hadronic Zγ production in the neutrino decay channel. Combining this measurement with our previous results using Z→ee and μμ yields the most stringent 95% C.L. limits to date on anomalous couplings: |h 30 Z | 40 Z |<0.06 (Λ=750GeV).