Antiprotonic atoms in gaseousH2and He and in liquidH2

Abstract

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 $\mathrm{nP}\to 1S$ x rays in liquid and gaseous hydrogen.