We search for a light scalar particle produced in single-photon decays of the Υ(3S) resonance through the process Υ(3S) → γ + A 0, A 0 → invisible. Such an object appears in Next-to-Minimal Supersymmetric extensions of the Standard Model, where a light CP-odd Higgs boson naturally couples strongly to b-quarks. If, in addition, there exists a light, stable neutralino, decays of A 0 could be preferentially to an invisible final state. We search for events with a single high-energy photon and a large missing mass, consistent with a 2-body decay of Υ(3S). We find no evidence for such processes in a sample of 122 × 10 6 Υ(3S) decays collected by the BABAR collaboration at the PEP-II B-factory, and set 90 % C.L. upper limits on the branching fraction B(Υ(3S) → γA 0) × B(A 0 → invisible) at (0.7 − 31) × 10 −6 in the mass range m A 0 ≤ 7.8 GeV. The results ar
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