Search for dark photon, axion-like particles, dark scalar, or light dark matter in Compton-like processes

TL;DR

This paper introduces a new method using Compton-like processes to search for various light dark matter particles, demonstrating that existing and future fixed target experiments can significantly improve detection sensitivities.

Contribution

It proposes a novel production mechanism for dark particles in Compton-like processes and evaluates the potential of fixed target experiments to detect these particles, including invisible ones.

Findings

Existing experiments can be competitive in dark particle searches.

Beam dump experiments' photon flux enhances sensitivity.

New limits on dark photon and axion-like particle couplings are established.

Abstract

We propose a novel way to search for the dark photon ($A'$), the axion-like pseudo-scalar ($a$), the dark scalar ($\phi$), and the light dark matter ($\chi$) in the Compton-like processes, $\gamma + e^- \rightarrow A'/a/\phi + e^-$ with $A'/a/\phi$ decaying into leptons, photons, or $\chi$'s (when permitted) for the mass ranges of $m_{A'/a/\phi} \leq$ 100 MeV/$c^2$ and $m_{\chi} \leq $ 50 MeV/$c^2$. We examine how the past, current, and future fixed target experiments can use this under-explored production mechanism of dark particles. We show that the existing and planned tagged photon beam fixed-target experiments (GlueX, LEPS2, LEPS, and FOREST) are competitive with the electron beam fixed target experiments, particularly for searching an invisible particle. We also show that the photon flux produced in the beam dump experiments increases the dark particle flux significantly and therefore the sensitivities of these experiments. By only considering the Compton-like processes, we determine the new limits and expected sensitivities for several beam dump and active beam dump experiments (E774, E141, KEK, Orsay, E137, NA64, BDX and LDMX) on the kinetic mixing parameter ($\epsilon$) between the dark photon and the Standard Model photon, the axion-like pseudo-scalar coupling to electrons ($g_{ae}$), the dark scalar coupling to electrons ($y_e$) and the dimensionless interaction strength ($y$) to light dark matter.