Experimental Test of the Theory of Muonic Atoms

Abstract

We have measured muonic x rays in the energy region 150 to 440 keV in nine elements with an absolute precision of 15 to 21 eV for transitions with small nuclear effects. Calculated transition energies were found to be consistently larger than those measured by an amount that varied from 15 \ifmmode\pm\else\textpm\fi{} 16 eV at 157 keV to 137 \ifmmode\pm\else\textpm\fi{} 22 eV at 438 keV. For these transitions, the principal correction to the Dirac energy is the vacuum polarization. The discrepancy, however, lies outside the expected validity of quantum-electrodynamic calculations and we are unable, at present, to offer an explanation for this effect.