Probing Neutral Triple Gauge Couplings with $Z^{\ast }\gamma (\nu \bar{\nu }\gamma )$ Production at Hadron Colliders

Abstract

We study probes of neutral triple gauge couplings (nTGCs) via $Z^{\ast }\gamma$ production followed by off-shell decays $Z^{\ast }\to \nu \bar{\nu }$ 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 $Z^{\ast }\gamma V^{\ast }$ ($V=Z,\gamma$) by matching them with the dimension-8 SMEFT operators. Our analysis includes new contributions enhanced by the large off-shell momentum of $Z^{\ast }$, beyond those of the conventional $Z\gamma V^{\ast }$ 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.

Comments: 25 pages (including supplemental material), only minor refinements, to match the version of PRD(letter)