Measurement of the positronium 1[sup 3]S[sub 1]-2[sup 3]S[sub 1] interval by continuous-wave two-photon excitation
Positronium is the quasi-stable bound system consisting of an electron and its anti-particle, the positron. Its energy levels can be explained to a high degree of accuracy by the electromagnetic interaction, affording an ideal test of the quantum electrodynamic (QED) theory of bound systems. In this pursuit, the authors have measured the 1[sup 3]S[sub 1]-2[sup 3]S[sub 1] interval in positronium by Doppler-free two-photon spectroscopy to be (1 233 607 216.4 [+-] 3.2) MHz. They employ continuous-wave (cw) excitation to eliminate the problems inherent with pulsed laser measurements of nonlinear transitions. Positronium atoms (Ps) generated in vacuum were excited to the 2S state using cw laser light built up to 2.5 kilowatts of circulating power in a resonant Fabry-Perot cavity. The excited state atoms were photoionized using a 532-nm pulsed laser and the liberated positrons counted as the cw laser was tuned relative to a reference line in molecular tellurium (Te[sub 2]) vapor. The fit of a detailed theoretical model to the measured line shape determines the Ps resonance frequency relative to the reference line. The Monte-Carlo model includes details of the excitation and detection geometry, the positronium velocity distribution, dynamic Stark shift, and gives excellent agreement with the measured line shapes. The quoted 2.6-ppb uncertainty is dominated by the measurement of the Ps line center relative to the Te[sub 2] reference line, with a 1.0-ppb contribution from a recent calibration of our Te[sub 2] cell relative to half of the hydrogen 1S-2S transition frequency. The measurement is an excellent agreement with theory and sufficiently accurate to provide a test of the as-yet-uncalculated [alpha][sup 4]R[sub [infinity]] QED correction.
- Research Organization:
- Stanford Univ., CA (United States)
- OSTI ID:
- 7014651
- Resource Relation:
- Other Information: Thesis (Ph.D.)
- Country of Publication:
- United States
- Language:
- English
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Measurement of the positronium 1[sup 3][ital S][sub 1]-2[sup 3][ital S][sub 1] interval by continuous-wave two-photon excitation
Measurement of the positronium 1/sup 3/S/sub 1/-2/sup 3/S/sub 1/ interval by Doppler-free two-photon spectroscopy