Search for a Neutral Boson in a Two-Body Decay ofK+→π+X0

Abstract

The momentum spectrum of the ${\pi }^{+}$ in stopping $K^{+}$ decays was measured by use of a high-resolution magnetic spectrometer to search for a discrete peak due to a neutral boson $X^0$ in a two-body decay $K^{+}\to {\pi }^{+}{X}^0$. An upper bound of the branching ratio $R(K^{+}\to {\pi }^{+}{X}^0)$ is presented for the mass range of $X^0$ from 10 to 300 MeV/${\mathit{c}}^2$.