We present a search for a non-Standard-Model invisible particle X0 in the mass range 0.1-1.8 GeV/c2 in B+→e+X0 and B+→μ+X0 decays. The results are obtained from a 711 fb-1 data sample that corresponds to 772×106BB pairs, collected at the Ψ(4S) resonance with the Belle detector at the KEKB e+e- collider. One B meson is fully reconstructed in a hadronic mode to determine the momentum of the lepton of the signal decay in the rest frame of the recoiling partner B meson. We find no evidence of a signal and set upper limits on the order of 10-6.
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