Probing axion-like particles at the Electron-Ion Collider

The Electron-Ion Collider (EIC), a forthcoming powerful high-luminosity facility, represents an exciting opportunity to explore new physics. In this article, we study the potential of the EIC to probe the coupling between axion-like particles (ALPs) and photons in coherent scattering. The ALPs can be produced via photon fusion and decay back to two photons inside the EIC detector. In a prompt-decay search, we find that the EIC can set the most stringent bound for m_a ≲ 20 GeV and probe the effective scales Λ ≲ 10⁵ GeV. In a displaced-vertex search, which requires adopting an EM calorimeter technology that provides directionality, the EIC could probe ALPs with m_a ≲ 1 GeV at effective scales Λ ≲ 10⁷ GeV. Combining the two search strategies, the EIC can probe a significant portion of unexplored parameter space in the 0.2 < m_a < 20 GeV mass range.