Test of charge-conjugation symmetry via microwave spectroscopy of positronium

The (Equation Presented) interval in positronium has been measured via microwave spectroscopy. This transition is strictly forbidden by charge conjugation invariance but may be observed in a magnetic field. Extrapolation of the Rabi frequencies obtained from spectral line shapes measured in different fields to the zero field case was used to test for a possible C-violating interaction with Hamiltonian HCV, characterized by the matrix element (Equation Presented).We obtain (Equation Presented) and (Equation Presented) (Equation Presented) components, respectively.