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Park, C.-S.; Kwon, Y.-J.; Adachi, I.; Ritter, M.; Schlueter, T. (2016): Search for a massive invisible particle X⁰ in B⁺ -> e⁺X⁰ and B⁺ -> μ⁺X⁰ decays. In: Physical Review D, Vol. 94, No. 1, 12003
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We present a search for a non-Standard-Model invisible particle X-0 in the mass range 0.1-1.8 GeV/c(2) in B+ -> e(+)X(0) and B+ -> mu X-+(0) decays. The results are obtained from a 711 fb(-1) data sample that corresponds to 772 x 10(6) B (B) over bar pairs, collected at the Upsilon(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).