Study of the reactionp+d→He3+x0

The missing-mass technique has been used to study the spectra of neutral mesons produced by 2- and 3-Gev protons in the reaction $p+d\to {\mathrm{He}}^3+x^0$. Cross sections ($\frac{d\sigma }{{d\Omega }_{\mathrm{c}.\mathrm{m}.\mathrm{}}}$) of about ${10}^{-34\mathrm{}}$ ${\mathrm{cm}}^2$/sr were observed for the $\pi$, $\eta$, and $\omega$ for 3-GeV protons. A peak with a much smaller cross section was observed at a mass of 956 MeV. We have tentatively identified this peak as the ${\eta }^{\prime }$. Cross sections for the $\pi$ and $\eta$ were nearly a factor of 10 larger at 2 GeV than at 3 GeV. Deviations from simple phase space were observed near the two-pion threshold in both 2-GeV and 3-GeV data. Details of the experimental method and of the results are presented.