Antiprotonic atoms in gaseous H 2 and He and in liquid H 2

Antiprotons were brought to rest in targets of gaseous ${\mathrm{H}}_{2}$ and gaseous He at temperatures of 30 K and also in a target of liquid ${\mathrm{H}}_{2}$. High-resolution x-ray detectors were used to measure the energies of x rays from $\overline{\mathrm{p}}$-He and to search for x rays from $\overline{\mathrm{p}}$-H. The $\overline{\mathrm{p}}$-He data are compared with similar measurements at different densities and with the theoretical predictions of Landua and Klempt. The $\overline{\mathrm{p}}$-H data provide upper limits for the yields of $\mathrm{nP}\ensuremath{\rightarrow}1S$ x rays in liquid and gaseous hydrogen.