Probing the Dark Sector with Dark Matter Bound States

Abstract

A model of dark sector where O(few GeV) mass dark matter particles χ are supplied by a lighter dark force mediator V, m_V ≪ m_χ, 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 χ, such as 0^(−+) and 1^(−−) states, η_D and Υ_D, is an important search channel. We show that e+e− → η_D + V or Υ_D + γ production at B-factories for α_D > 0.1 is sufficiently strong to result in multiple pairs of charged leptons and pions via η_D → 2V → 2(l^+l^−) and Υ_D → 3V → 3(l+l−) (l = e, µ, π). 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^− → χχ¯ + nV , resulting in missing energy and multiple leptons, will further improve the sensitivity to self-interacting dark matter.