Invisible Quarkonium Decays as a Sensitive Probe of Dark Matter

Abstract

We examine in a model-independent manner the measurements that can be performed at B-factories with sensitivity to dark matter. If a singlet scalar, pseudo-scalar, or vector is present and mediates the Standard Model - dark matter interaction, it can mediate invisible decays of quarkonium states such as the $Υ$, $J/Ψ$, and $η$. Such scenarios have arisen in the context of supersymmetry, extended Higgs sectors, solutions the supersymmetric $μ$ problem, and extra U(1) gauge groups from grand unified theories and string theory. Existing B-factories running at the $Υ(4S)$ can produce lower $Υ$ resonances by emitting an Initial State Radiation (ISR) photon. Using a combination of ISR and radiative decays, the initial state of an invisibly decaying quarkonium resonance can be tagged, giving sensitivity to the spin and CP-nature of the particle that mediates standard model-dark matter interactions. These measurements can discover or place strong constraints on dark matter scenarios where the dark matter is approximately lighter than the $b$-quark. For the decay chains $Υ(nS) \to π^+ π^- Υ(1S)$ (n=2,3) we analyze the dominant backgrounds and determine that with $400 fb^{-1}$ collected at the $Υ(4S)$, the B-factories can limit $BR(Υ(1S) \to invisible) \lsim 0.1%$.