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We report experiments in which positronium (Ps) atoms, optically excited to Rydberg states with principal quantum numbers n in the range 18-25, were selectively ionized by both static and pulsed electric fields. The experiments were modeled using Monte Carlo simulations that include tunnel ionization rates calculated for hydrogen and scaled by the Ps reduced mass. Our measurements exhibit a small disagreement with the calculated tunnel ionization rates. Despite this we show that the electric fields in which different Ps states are ionized are sufficiently separated to allow selective field-ionization methods to be used in typical experimental conditions.

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The electron magnetic moment in Bohr magnetons, −µ/µB = 1.001 159 652 180 59 (13) [0.13 ppt], is consistent with a 2008 measurement and is 2.2 times more precise. The most precisely measured property of an elementary particle agrees with the most precise prediction of the Standard Model (SM) to 1 part in 10 12 , the most precise confrontation of all theory and experiment. The SM test will improve further when discrepant measurements of the fine structure constant α are resolved, since the prediction is a function of α. The magnetic moment measurement and SM theory together predict α −1 = 137.035 999 166 (15) [0.11 ppb]

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