The n = 2 fine-structure transitions in positronium have been measured by observation of increased Lyman-a radiation at microwave induced resonances. We used an accelerator based slow positron beam to produce positronium in the 2 3 5'i excited state inside a waveguide. Our results are v 0 = 18499.65 ± 1.20±4.00 MHz, vi-13012.42±0.67±1.54 MHz, and v 2 =8 624.38 ±0.54 ± 1.40 MHz for the 2 3 S'i-* 2 3 Po,\,2 transition frequencies, respectively. The first error is statistical and the second is systematic. This is in agreement with recent bound state QED calculations.
A compensated Penning trap has been used to measure the modified cyclotron frequency v: and the magnetron frequency v, of single trapped 3He+ and HZ ions. From the ratio of the sum of these frequencies we obtain a mass ratio m$He+)/m(H,') = 1.496441 095(6) in accordance with published values.
We describe an experimental setup to determine the cyclotron frequencies of ions confined in a Penning trap by resonant excitation of the ions eigenfrequencies and a time-of-flight detection of the resonances. Systematic shifts from trap- and B-field imperfections are discussed and methods to minimize those effects in our experiment are presented. Results on the mass ratio for 4He/D2 and 3He/H2 demonstrate the experimentally obtained precision in the ppb range, which might be further improved by modification of our apparatus.
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