X-Rays from Mesic Atoms

Abstract

Several authors' have discussed the possible formation of a mesic atom composed of a positively charged nucleus to which a negative pion or muon is bound in a Bohr-like orbit. There have been at least two experiments performed which gave indirect evidence for such phenomena. Here we have found direct evidence for $π$-mesic atom formation with the nuclei of carbon, oxygen, and beryllium. For $Z$ < 10 the nuclear radius is small compared to the radii of even the lowest mesic orbits, and hence a simple Coulomb potential should suffice for calculating the expected energy levels. Such a calculation for the 2$p$—1$s$ is transition (assuming a pion mass = 276 m_e) gives quantum energies of 100 kev in carbon, 178 kev in oxygen, and 44.3 kev in beryllium.