Probing the scale of new physics in the ZZγ coupling at e+e− colliders The work of JE was supported in part by United Kingdom STFC Grant ST/P000258/1, in part by the Estonian Research Council via a Mobilitas Pluss grant, and in part by the TDLI distinguished visiting fellow programme. The work of HJH and RQX was supported in part by the National NSF of China (11675086, 11835005). HJH is also supported in part by the CAS Center for Excellence in Particle Physics (CCEPP), by the National Key R&D Program of China ( 2017YFA0402204), by the Shanghai Laboratory for Particle Physics and Cosmology (11DZ2260700), and by the Office of Science and Technology, Shanghai Municipal Government (16DZ2260200)
John Ellis (
Department of Physics, Kings College London, Strand, London WC2R 2LS, UK; Theoretical Physics Department, CERN, CH-1211 Geneva 23, Switzerland; NICPB, Rävala 10, 10143 Tallinn, Estonia,
Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China); Shao-Feng Ge (
Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China); Hong-Jian He (
Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China,
Institute of Modern Physics, Tsinghua University, Beijing 100084, China; Center for High Energy Physics, Peking University, Beijing 100871, China); Rui-Qing Xiao (
Tsung-Dao Lee Institute & School of Physics and Astronomy, Shanghai Jiao Tong University, Shanghai 200240, China)
The
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
followed by
decays, at future
colliders including the CEPC, FCC-ee, ILC and CLIC. We demonstrate how angular distributions of the final-state mono-photon and leptons can play a key rôle in suppressing SM backgrounds. We further demonstrate 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.
