American Physical Society, Physical Review Letters, 25(103)
DOI: 10.1103/physrevlett.103.251801
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7 pages, 3 postscript figures, submitted to Physical Review Letters ; We search for invisible decays of the Upsilon(1S) meson using a sample of 91.4 x 10^{6} Upsilon(3S) mesons collected at the BaBar/PEP-II B-factory. We select events containing the decay Upsilon(3S) -> pi+ pi- Upsilon(1S) and search for evidence of an undetectable Upsilon(1S) decay recoiling against the dipion system. We set an upper limit on the branching fraction BR(Upsilon(1S) -> invisible)