Search for Production of Invisible Final States in Single-Photon Decays of $Υ(1S)$

Abstract

We search for single-photon decays of the $Υ(1S)$ resonance, $Υ→γ+$ invisible, where the invisible state is either a particle of definite mass, such as a light Higgs boson $A^0$, or a pair of dark matter particles, $χ\overline{χ}$. Both $A^0$ and χ are assumed to have zero spin. We tag $Υ(1S)$ decays with a dipion transition $Υ(2S)→π^{+}π^{−}Υ(1S)$ and look for events with a single energetic photon and significant missing energy. We find no evidence for such processes in the mass range $m_{A^{0}}≤9.2 GeV$ and $m_{χ}≤4.5 GeV$ in the sample of $98×10^{6} Υ(2S)$ decays collected with the BABAR detector and set stringent limits on new physics models that contain light dark matter states.Physic