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Probing neutral triple gauge couplings via ZZ production at e+e− colliders with machine learning

John Ellis1,*, Hong-Jian He2,3,4,†, Rui-Qing Xiao5,‡, and Shi-Ping Zeng2,§

  • *Contact author: john.ellis@cern.ch
  • †Contact author: hjhe@sjtu.edu.cn
  • ‡Contact author: xiaoruiqing@pku.edu.cn
  • §Contact author: spzeng@sjtu.edu.cn
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Phys. Rev. D 113, 075005 – Published 3 April, 2026

DOI: https://doi.org/10.1103/w9wn-fxkc

Abstract

Neutral triple gauge couplings (nTGCs) first arise from the dimension-8 operators of the Standard Model effective field theory (SMEFT), rather than the dimension-4 SM Lagrangian and dimension-6 SMEFT operators, opening up a unique window for probing new physics at the dimension-8 level. In this work, we formulate the nTGC form factors of ZZV* (V=Z, γ) that are compatible with the spontaneous breaking of the SU(2)⊗U(1) electroweak gauge symmetry and consistently match the dimension-8 nTGC operators in the broken phase. We study the sensitivities for probing both the ZZV* form factors and the corresponding new physics scales through ZZ production (with visible/invisible fermionic Z decays) at high energy e+e− colliders including CEPC, FCC-ee, LCF, ILC, and CLIC. In particular, we identify the dimension-8 operator that contributes to the pure triple Z boson coupling ZZZ* alone, but not the mixed ZZγ* coupling. We further study the correlations between probes of the ZZZ* and ZZγ* couplings. Using machine learning, we show that angular distributions of the final-state fermions can play key roles in suppressing the SM backgrounds. The sensitivities can be further improved by using polarized e∓ beams, and we find that the optimal sensitivity bounds on the nTGC correlations are given by the mixed setting including both the unpolarized operation and the follow-up polarized operation. We demonstrate that machine learning is advantageous for handling the 4-body final states from ZZ decays and improves significantly the sensitivity reaches of probes of nTGCs in e+e− collisions. We find that nTGC new physics scales can be probed up to the multi-TeV scale at the proposed e+e− colliders.

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Phys. Rev. D 113, 075005– Published 3 April, 2026
  • Received 4 September 2025
  • Accepted 12 February 2026
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