Invisible and displaced dark matter signatures at Belle II

TL;DR

This paper highlights the importance of a displaced vertex trigger at Belle II for detecting dark matter signatures involving missing energy and displaced particles, demonstrating improved sensitivity for certain models.

Contribution

It proposes a displaced vertex trigger to enhance Belle II's ability to detect dark matter signatures and evaluates its effectiveness in a specific inelastic dark matter model.

Findings

Displaced vertex trigger significantly improves detection sensitivity.

Certain dark matter parameter space regions become accessible with this method.

The study provides detailed relic density calculations for the model.

Abstract

Many dark matter models generically predict invisible and displaced signatures at Belle II, but even striking events may be missed by the currently implemented search programme because of inefficient trigger algorithms. Of particular interest are final states with a single photon accompanied by missing energy and a displaced pair of electrons, muons, or hadrons. We argue that a displaced vertex trigger will be essential to achieve optimal sensitivity at Belle II. To illustrate this point, we study a simple but well-motivated model of thermal inelastic dark matter in which this signature naturally occurs and show that otherwise inaccessible regions of parameter space can be tested with such a search. We also evaluate the sensitivity of single-photon searches at BaBar and Belle II to this model and provide detailed calculations of the relic density target.