New channel to search for dark matter at Belle II

TL;DR

This paper proposes a novel search channel at Belle II for dark matter involving a disappearing positron track, which could explore new parameter space beyond existing methods by detecting positron scatterings producing dark matter.

Contribution

The paper introduces a new experimental channel at Belle II for dark matter detection, utilizing positron scatterings with the calorimeter to identify dark matter interactions.

Findings

The new channel can probe previously unexplored dark matter parameter space.

It surpasses existing Belle II mono-photon searches and NA64 constraints in sensitivity.

The method effectively suppresses backgrounds from photons and neutrons.

Abstract

We propose a new ``disappearing positron track'' channel at Belle II to search for dark matter, in which a positron that is produced at the primary interaction vertex scatters with the electromagnetic calorimeter to produce dark matter particles. Such scatterings can occur via either annihilation with atomic electrons, or the bremsstrahlung process with target nuclei. The main backgrounds are due to photons and neutrons that are produced in the same scatterings and then escape detection. We require a large missing energy and further veto certain activities in the KLM detector to suppress such backgrounds. To illustrate the sensitivity of the new channel, we consider a new physics model where dark matter interacts with the standard model via a dark photon, which decays predominantly to dark matter; we find that our proposed channel can probe some currently unexplored parameter space, surpassing both the mono-photon channel at Belle II and the NA64 constraints.