Search for a massive invisible particle X0 in B+→e+X0 and B+→μ+X0 decays

Abstract

We present a search for a non-Standard-Model invisible particle X0 in the mass range 0.1–1.8 GeV/c^2 in B + -> e+X0 and B+ -> mu+ X0. The results are obtained from a 711 fb^−1 data sample thatcorresponds to 772 × 10^6BBbar 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 thelepton 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.