# Dark Spectroscopy

## TL;DR

This paper proposes a novel method for probing the mass structure of dark sectors in particle physics using mono-photon spectroscopy at lepton colliders, enabling the study of dark sector resonances.

## Contribution

It introduces a new spectroscopy technique for dark sectors via mono-photon energy measurements at lepton colliders, demonstrated with multiple dark sector models.

## Key findings

- Mono-photon energy correlates with dark sector resonance structures.
- Method applicable at Belle II, BES-III, and future colliders.
- Potential to uncover complex dark sector spectra.

## Abstract

Rich and complex dark sectors are abundant in particle physics theories. Here we propose performing spectroscopy of the mass structure of dark sectors via mono-photon searches at lepton colliders. The energy of the mono-photon tracks the invariant mass of the invisible system it recoils against, which enables studying the resonance structure of the dark sector. We demonstrate this idea with several well-motivated models of dark sectors. Such spectroscopy measurements could potentially be performed at Belle II, BES-III and future low-energy lepton colliders.