arXiv : Probing the Scale of New Physics in the $ZZ\gamma$ Coupling at $e^+e^-$ Colliders

Ellis, John; Ge, Shao-Feng; He, Hong-Jian; Xiao, Rui-Qing

doi:10.1088/1674-1137/44/6/063106

Article
Report number	arXiv:1902.06631 ; KCL-PH-TH/2019-11 ; CERN-TH/2019-008 ; CERN-TH-2019-008 ; IPMU19-0021
Title	Probing the Scale of New Physics in the $ZZ\gamma$ Coupling at $e^+e^-$ Colliders
Related title	Probing the scale of new physics in the ZZγ coupling at e+e− colliders
Author(s)	Ellis, John (King's Coll. London ; CERN ; NICPB, Tallinn ; Tsung-Dao Lee Inst., Shanghai) ; Ge, Shao-Feng (Tsung-Dao Lee Inst., Shanghai ; Tokyo U., IPMU ; UC, Berkeley ; Shanghai Jiaotong U.) ; He, Hong-Jian (Tsung-Dao Lee Inst., Shanghai ; Shanghai Jiaotong U. ; Tsinghua U., Beijing ; Peking U., CHEP) ; Xiao, Rui-Qing (Tsung-Dao Lee Inst., Shanghai ; Shanghai Jiaotong U.)
Publication	2020-06-09
Imprint	2019-02-18
Number of pages	32
Note	* Temporary entry * * Temporary entry * Final Journal Version, 53 pages [12 Figs (30 plots), 7 Tables]. Extended version, all conclusions and results unchanged, clarifications & references added
In:	Chin. Phys. C 44 (2020) 063106
DOI	10.1088/1674-1137/44/6/063106 (publication)
Subject category	hep-ph ; Particle Physics - Phenomenology
Abstract	The $ZZ\gamma$ triple neutral gauge couplings are absent in the Standard Model (SM) at the tree level. They receive no contributions from dimension-6 effective operators, but can arise from effective operators of dimension-8. We study the scale of new physics associated with such dimension-8 operators that can be probed by measuring the reaction $e^+e^-\to Z\gamma$, followed by $Z \to \ell\bar{\ell},\nu\bar{\nu}$ decays, at future $e^+e^-$ colliders including the ILC, CEPC, FCC-ee and CLIC. We demonstrate how angular distributions of the final state mono-photon and leptons can play a key role in suppressing SM backgrounds. We further show that using electron/positron beam polarizations can significantly improve the signal sensitivities. We find that the dimension-8 new physics scale can be probed up to the multi-TeV region at such lepton colliders.
Copyright/License	preprint: (License: arXiv nonexclusive-distrib 1.0)

$\it Illustration of the kinematical structure of the reaction $\,e^+e^-\!\!\to Z\ga\,$ followed by the leptonic decay $\,Z\!\to \ell^+\ell^-$\, in the laboratory frame ($\,e^-e^+$\! collision frame).$ $\it Normalized angular distributions in the polar scattering angle $\theta$ in the laboratory frame for different collision energies,} $\sqrt{s}=(250\,\text{GeV}, 500\,\text{GeV}, 1\,\text{TeV}, 3\,\text{TeV})$. {\it In each plot, the black, red and blue curves denote the contributions from the SM, the ${\cal O}(\cut^{-4})$ and ${\cal O}(\cut^{-8})$ terms, respectively. We use a polar angle cut $\,\delta=0.2\,$ for illustration.$ $\it Normalized angular distributions in the polar scattering angle $\theta$ in the laboratory frame for different collision energies,} $\sqrt{s}=(250\,\text{GeV}, 500\,\text{GeV}, 1\,\text{TeV}, 3\,\text{TeV})$. {\it In each plot, the black, red and blue curves denote the contributions from the SM, the ${\cal O}(\cut^{-4})$ and ${\cal O}(\cut^{-8})$ terms, respectively. We use a polar angle cut $\,\delta=0.2\,$ for illustration.$ Show more plots

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