We investigated the missing-mass spectra at the $2\pi$ threshold in the reaction $p+d\to {\mathrm{He}}^3+X^0$ and searched for the resonance reported at a mass of 450 MeV using 2-GeV protons. The shape of the missing-mass spectra below the ${\eta }^0$ mass deviates from two-body phase space and was similar to that obtained with 3-GeV protons. If a 450-MeV resonance exists, the c.m. cross section for producing it in this reaction is less than 10.8 × ${10}^{-36\mathrm{}}$ and 5.7 × ${10}^{-36\mathrm{}}$ ${\mathrm{cm}}^2$/sr with 2- and 3-GeV protons, respectively.

• Received 31 January 1972

DOI:https://doi.org/10.1103/PhysRevLett.28.1215