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Abstract:
We report new measurements of the positronium (Ps) 23S1→23PJ fine-structure intervals, νJ (J=0,1,2). In the experiments, Ps atoms, optically excited to the radiatively metastable 23S1 level, flew through microwave radiation fields tuned to drive transitions to the short-lived 23PJ levels, which were detected via the time spectrum of subsequent ground-state Ps annihilation radiation. Both the ν1 and ν2 line shapes were found to be asymmetric, which, in the absence of a complete line-shape model, prevents accurate determination of these fine-structure intervals. Conversely, the ν0 line shape did not exhibit any significant asymmetry; the observed interval, however, was found to disagree with QED theory by 4.2 standard deviations.
