Prospects for probing light photophobic axion-like particles via displaced vertex signals at the CEPC

TL;DR

This paper explores the potential of the CEPC collider to detect light, long-lived axion-like particles through displaced vertex signals, expanding the search capabilities beyond current collider experiments.

Contribution

It provides a detailed analysis of the discovery prospects for photophobic ALPs at the CEPC, focusing on specific production and decay channels with Monte Carlo simulations.

Findings

CEPC can probe ALP couplings in specific mass ranges.

Displaced vertex signals offer a promising detection method.

Results complement existing collider searches.

Abstract

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 via displaced vertex signals at the CEPC with the center-of-mass energy $\sqrt{s}=91.2 $ GeV and integrated luminosity $\mathcal{L}=$ $100$ ab$^{-1}$. After comparing several possible single-production processes of the photophobic ALP, we focus on the dominant process $e^+ e^- \to Z \to a \gamma $, with the ALP $a$ subsequently decaying into a pair of displaced charged leptons. Dedicated Monte Carlo simulations are performed for the $\mu^+ \mu^- \gamma$ and $\tau_h^+ \tau_h^- E\mkern-10.5 mu/_T \gamma$ signals. For the $\mu^+\mu^-\gamma$ signal, the CEPC is sensitive to the parameter region $g_{aWW} \in [1.27\times10^{-3},6.80\times10^{-1}]~\mathrm{TeV}^{-1}$ for $m_a \in [1,4]~\mathrm{GeV}$. For the $\tau_h^+\tau_h^-E\mkern-10.5 mu/_T\gamma$ signal, the accessible region is $g_{aWW} \in [7.00\times10^{-4},9.40\times10^{-3}]~\mathrm{TeV}^{-1}$ with $m_a \in [4,9]~\mathrm{GeV}$. These results demonstrate the strong potential of the CEPC to explore light long-lived ALPs via displaced vertex signals, providing complementary coverage to existing searches at the LEP and LHC, as well as to the projected reach of the HL-LHC.