2026/03/14 by Chong-Xing Yue, Xin-Yang Li
Physics and Astronomy · #hep-ph
26 pages, 11 figures, 4 tables, to be published in Chinese Physics C
arxiv created 2026/07/30 · arxiv updated 2026/07/31
In recent years, long-lived particles (LLPs) have attracted increasing attention in searches for physics beyond the Standard Model (SM). In this paper, we investigate the discovery prospects for light, long-lived ALPs predicted by the photophobic ALP scenario through displaced-vertex signals at the CEPC, with a center-of-mass energy of √(s)=91.2 GeV and an integrated luminosity of L= 100 ab-1. After comparing several possible single-production processes for the photophobic ALP, we focus on the dominant process e+ e- → Z → a γ, in which the ALP a subsequently decays into a pair of charged leptons at a displaced vertex. Dedicated Monte Carlo simulations are performed for the μ+ μ- γ and τh+ τh- E\mkern-10.5 mu/T γ signals. For the μ+μ-γ signal, the CEPC is sensitive to the parameter region gaWW ∈ [1.27×10-3,6.80×10-1]~TeV-1 for ma ∈ [1,4]~GeV. For the τh+τh- E\mkern-10.5 mu/T γ signal, the accessible region is gaWW ∈ [7.00×10-4,9.40×10-3]~TeV-1 for ma ∈ [4,9]~GeV. These results demonstrate the substantial potential of the CEPC to explore light, long-lived ALPs through displaced-vertex signals, providing complementary coverage to existing searches at LEP and the LHC, as well as to the projected reach of the HL-LHC.