Fusing photons into nothing, a new search for invisible ALPs and Dark Matter at Belle II

TL;DR

This paper proposes a novel search method at Belle II for axion-like particles decaying invisibly, which could improve detection sensitivity across a broad mass range and has implications for Dark Matter models.

Contribution

It introduces a new $e^+e^-+ ext{invisible}$ search channel with specialized kinematic variables, enhancing the detection prospects for ALPs compared to traditional methods.

Findings

Potential to improve ALP detection sensitivity across all mass ranges.

Significant background suppression using dedicated kinematic variables.

Implications for Dark Matter freeze-out via ALP-mediated annihilations.

Abstract

We consider an axion-like particle coupled to the Standard Model photons and decaying invisibly at Belle II. We propose a new search in the $e^+e^-+\text{invisible}$ channel that we compare against the standard $\gamma+\text{invisible}$ channel. We find that the $e^+e^-+\text{invisible}$ channel has the potential to ameliorate the reach for the whole ALP mass range. This search leverages dedicated kinematic variables which significantly suppress the Standard Model background. We explore the implications of our expected reach for Dark Matter freeze-out through ALP-mediated annihilations.