Probing the Dark Sector with Dark Matter Bound States

TL;DR

This paper explores how bound states of dark matter particles in a dark sector can be detected at electron-positron colliders, providing new constraints and search strategies for dark matter models involving light mediators.

Contribution

It introduces the idea that dark matter bound state production and decay can serve as a novel detection channel at B-factories, and derives constraints from existing experimental data.

Findings

Bound states like η_D and Υ_D can produce detectable multi-lepton and pion final states.

Existing B-factory data constrains the parameter space of dark sector models.

Proposed new search strategies can improve sensitivity to dark matter with light mediators.

Abstract

A model of dark sector where $O({\rm few~GeV})$ mass dark matter particles $\chi$ couple to a lighter dark force mediator $V$, $m_V \ll m_\chi$, is motivated by the recently discovered mismatch between simulated and observed shapes of galactic haloes. Such models, in general, provide a challenge for direct detection efforts and collider searches. We show that for a large range of coupling constants and masses, the production and decay of the bound states of $\chi$, such as $0^{-+}$ and $1^{--}$ states, $\eta_D$ and $ \Upsilon_D$, is an important search channel. We show that $e^+e^-\to \eta_D +V$ or $\Upsilon_D +\gamma$ production at $B$-factories for $\alpha_D > 0.1$ is sufficiently strong to result in multiple pairs of charged leptons and pions via $\eta_D\to 2V \to 2(l^+l^-)$ and $\Upsilon_D\to 3V \to 3(l^+l^-)$ $(l=e,\mu,\pi)$. The absence of such final states in the existing searches performed at \babar\ and Belle sets new constraints on the parameter space of the model. We also show that a search for multiple bremsstrahlung of dark force mediators, $e^+e^-\to \chi\bar\chi+nV$, resulting in missing energy and multiple leptons, will further improve the sensitivity to self-interacting dark matter.