Search for narrow states in the inclusive $\gamma$-ray spectra resulting from antiproton annihilations at rest in liquid hydrogen and deuterium

The energy spectrum of $\gamma$ rays produced in proton-antiproton annihilation at rest in hydrogen and deuterium has been measured with good energy resolution and high statistics. The data were taken using the PS183 magnetic pair spectrometer at CERN's Low Energy Antiproton Ring. A detailed search of the $\gamma$ spectrum yielded no evidence of $\gamma$ transitions to narrow states with widths consistent with the spectrometer resolution. In hydrogen, upper limits (95% C.L.) are obtained for the yield of narrow states of (2-5)×${10}^{-4\mathrm{}}$ for states below 1700 MeV/${\mathit{c}}^2$, and (5-10)×${10}^{-4\mathrm{}}$ for states between 1700 and 1800 MeV/${\mathit{c}}^2$. In deuterium, the corresponding upper limits are (1-7)×${10}^{-3\mathrm{}}$ for masses between 700 and 1730 MeV/${\mathit{c}}^2$, and (1-2)×${10}^{-3\mathrm{}}$ for masses between 1750 and 1835 MeV/${\mathit{c}}^2$. These results contradict reports of the observation of narrow lines made by previous experiments.