Strong interaction and mass measurements using antiprotonic atoms

X-ray transition energies of antiprotonic atoms formed in targets of ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$, ${}_{}{}^7{}_{}{}^{}\mathrm{Li}$, C, Si, P, Fe, Y, Zr, Cs, and Yb have been measured. Level shifts and widths due to the strong interaction were determined. A phenomenological fit to the data using an optical-model potential proportional to the nuclear matter density and to an effective $\overline{p}$-nucleus $s$-wave scattering length yielded [$(0.85\mathrm{}\pm 0.38)+i(2.66\pm 0.28)$] fm for the effective scattering length. In addition, the mass of the antiproton was determined to be 938.229 ± 0.049 MeV from the observed energies of the $\overline{p}$ x-ray transitions unperturbed by the strong interaction.