Axion-like Particle Search with a Light-Shining-Through-Walls Setup at a $γ$-$γ$ Collider

Abstract

In this work, we have explored a practical extension of the conventional light-shining-through-walls technique by making direct use of the high-intensity $γ$-ray beam available at a $γ$-$γ$ collider. The energetic and highly collimated photon flux produced via inverse Compton scattering naturally provides an efficient ALP production stage, while the addition of a regeneration region downstream enables a complete LSW configuration without introducing new experimental complexities. This approach therefore represents an experimentally simple and infrastructure-compatible method for enhancing laboratory sensitivity to axion-like particles. Under conservative assumptions, we find that one year of operation can probe ALP-photon couplings down to $g_{aγγ}\simeq 3.82\times 10^{-5} \,\mathrm{GeV^{-1}}$ for $m_a\lesssim 0.1 \,\mathrm{eV}$ when an additional magnetic region is included upstream of the beam dump, improving upon previous laboratory LSW limits by up to an order of magnitude.

Figures (3)

• Figure 1: Schematic of the $\gamma$-$\gamma$ collider. The $200\,\mathrm{MeV}$ electrons will be deflected by a deflected magnetic field $\vec{B_0}$ to adjust their direction. The high-energy $\gamma$-rays are generated through the inverse Compton scatterings between the electrons and low-energy photons zhou2025estimationinversecomptonscattering. The high-energy $\gamma$-ray will pass through the magnetic field $\vec{B_0}$ and be converted into ALPs by the Primakoff effect.
• Figure 2: Schematic layout of the light-shining-through-walls setup implemented at the $\gamma$-$\gamma$ collider. High-energy $\gamma$ rays produced via inverse Compton scattering first traverse the magnetic-field region $\vec{B}_0$ (and optionally an additional region $\vec{B}_1$), where a fraction of the photons convert into axion-like particles (ALPs) through the Primakoff effect. The primary $\gamma$-ray beam is removed by a beam dump system before reaching the wall, so that the wall is not irradiated by high-energy photons. The wall serves only to absorb residual or scattered photons, while ALPs pass through unimpeded. Downstream of the wall, a second magnetic-field region $\vec{B}_2$ enables photon regeneration via the inverse Primakoff effect. The Photon Detector records regenerated photons behind the wall.
• Figure 3: Comparison of the projected sensitivity of our setup (red and blue) with other LSW experiments, including EuXFEL Halliday:2024lca, Inada Inada:2016jzh, NA64 NA64:2020qwq, ALPS Ehret:2010mh, and NOMAD NOMAD:2000usb. The improvement, particularly in the sub-eV to eV mass range, arises mainly from the substantially enhanced photon energy provided by the $\gamma$-ray source. The sensitivity that uses only deflection magnetic field $\vec{B_0}$ is shown in blue, and the sensitivity that adds an additional magnetic field $\vec{B_1}$ inside the $\gamma$-$\gamma$ collider is shown in red.