Search For Narrow Nbarn States Near Threshold

A missing-mass experiment in $\mathrm{pd}\ensuremath{\rightarrow}\mathrm{NX}$, where $X$ is the system whose mass ${M}_{X}$ is measured, was performed for interactions of antiprotons at rest and in flight below 500 MeV/c. The 4-standard-deviation upper limit for the production of narrow states, in the mass interval ${M}_{X}=1650\ensuremath{-}1930$ MeV/${\mathit{c}}^{2}$, is 2 mb for annihilations in flight and 0.3% of the annihilations at rest.