Probing Neutral Triple Gauge Couplings with $Z^* \gamma\, (\nu \bar \nu \gamma)$ Production at Hadron Colliders

TL;DR

This paper investigates the potential to probe neutral triple gauge couplings at hadron colliders through $Z^* o uar{ u}$ decays, introducing a new form factor approach for off-shell vertices and assessing sensitivity at current and future colliders.

Contribution

It develops a novel form factor formulation for off-shell $Z^* o uar{ u}$ vertices in the context of SMEFT, enhancing the analysis of nTGCs beyond on-shell approximations.

Findings

Enhanced sensitivity to nTGCs at 100TeV colliders.

New form factor formulation for off-shell vertices.

Comparison with existing LHC measurements shows improved constraints.

Abstract

We study probes of neutral triple gauge couplings (nTGCs) via $Z^*\gamma$ production followed by off-shell decays $Z^*\to\nu\bar{\nu}$ at the LHC and future $pp$ colliders, including both CP-conserving (CPC) and CP-violating (CPV) couplings. We present the dimension-8 SMEFT operators contributing to nTGCs and derive the correct form factor formulation for the off-shell vertices $Z^*\gamma V^*$ ($V=Z,\gamma$) by matching them with the dimension-8 SMEFT operators. Our analysis includes new contributions enhanced by the large off-shell momentum of $Z^*$, beyond those of the conventional $Z\gamma V^*$ vertices with on-shell $Z\gamma$. We analyze the sensitivity reaches for probing the CPC/CPV nTGC form factors and the new physics scales of the dimension-8 nTGC operators at the LHC and future 100TeV $pp$ colliders. We compare our new predictions with the existing LHC measurements of CPC nTGCs in the $\nu\bar\nu\gamma$ channel and demonstrate the importance of our new method.