Signatures of the anomalous $Zγ$ and ZZ production at the lepton and hadron Colliders

TL;DR

Addresses whether anomalous neutral triple gauge couplings ($ZZZ$, $ZZ\gamma$, $Z\gamma\gamma$) can reveal New Physics, using an effective Lagrangian approach constrained by Lorentz invariance, U(1)em, and Bose statistics. It develops a hermitian, gauge-invariant description of these couplings and analyzes their CP properties, illustrating a simple heavy-fermion loop model that yields predictive relations among couplings and shows that neutral vertices arise from higher-dimension operators. The authors compute NP helicity amplitudes for $f\bar f \to ZZ$ and $f\bar f \to Z\gamma$, studying their impact on observables at LEP2, a 500 GeV linear collider, Tevatron, and LHC, including interference patterns and polarization effects. They argue for analysis strategies that avoid ad hoc form factors by binning in invariant mass to enable cross-collider comparisons, guiding experimental constraints on the neutral gauge sector. Overall, the work provides a framework and practical guidance for probing neutral gauge structure and constraining New Physics through collider experiments.

Abstract

The possible form of New Physics (NP) interactions affecting the ZZZ, $ZZ γ$ and $Zγγ$ vertices, is critically examined. Their signatures and the possibilities to study them, through ZZ and $Zγ$ production, at the e^-e^+ Colliders LEP and LC and at the hadronic Colliders Tevatron and LHC, are investigated. Experimental limits obtained or expected on each coupling are collected. A simple theoretical model based on virtual effects due to some heavy fermions is used for acquiring some guidance on the plausible forms of these NP vertices. In such a case specific relations among the various neutral couplings are predicted, which can be experimentally tested and possibly used to constrain the form of the responsible NP structure.

Figures (9)

• Figure 1: Feynman rule for the general $V_1V_2V_3$ vertex.
• Figure 2: Standard and anomalous contributions to the unpolarized $e^-e^+ \to ZZ$ cross section at LEP.
• Figure 3: Standard and anomalous contributions to the unpolarized $e^-e^+ \to Z \gamma$ cross sections at LEP.
• Figure 4: Standard and anomalous contributions to unpolarized $e^-e^+ \to ZZ$ cross sections at an LC.
• Figure 5: Standard and anomalous contributions to unpolarized $e^-e^+ \to Z\gamma$ cross sections at an LC.