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

Abstract

We search for single-photon decays of the Υ ( 1 S ) 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 ¯¯¯ χ . Both A 0 and χ are assumed to have zero spin. We tag Υ ( 1 S ) decays with a dipion transition Υ ( 2 S ) → π + π − Υ ( 1 S ) 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 ( 2 S ) decays collected with the BABAR detector and set stringent limits on new physics models that contain light dark matter states.