Search for Light Short-Lived Particles in Radiative Upsilon Decays

Evidence for the possible production, and rapid decay into e⁺e^- pairs, of a new, light particle in heavy-ion collisions motivates the reexamination of searches for light particles in upsilon decays. We have searched for the decay Υ(1S)→γ+α, where α subsequently decays into an e⁺e^- pair in the detector. We observe no evidence for this decay, and obtain an upper limit for the branching ratio. We also show that our limit excludes the possibility of short-lived axions within the original axion model.