Search for a massive invisible particle $X^0$ in $B^{+}\to e^{+}{X}^0$ and $B^{+}\to \hat{I}{¼}^{+}{X}^0$ decays

Abstract

We present a search for a non-Standard-Model invisible particle $X^0$ in the mass range $0.1\text{-}1.8\mathrm{GeV}/c^2$ in $B^{+}\to e^{+}{X}^0$ and $B^{+}\to \hat{I}{¼}^{+}{X}^0$ decays. The results are obtained from a $711{\mathrm{fb}}^{-1}$ data sample that corresponds to $772\times 10^{6}B\bar{B}$ pairs, collected at the $\hat{I}\yen (4S)$ 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 $10^{-6}$.

8 pages, 4 figures, 3 tables