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    "title": "Positronium microwave field diagnostics and fine-structure measurement with a redesigned apparatus",
    "summary": "Sheldon and colleagues observed that the apparent positronium 2³S₁ → 2³P₂ transition frequency changed when a free-space microwave horn was rotated, even when the spectral lines showed little measurable asymmetry. They then measured the interval in a redesigned waveguide apparatus with reduced chamber reflections, reversed microwave directions and a retroreflected excitation laser. Averaging the two directions gave 8627.94±0.30(stat)±0.91(syst) MHz, within 1.3 standard deviations of the cited QED value. These experiments established practical diagnostics for microwave-field distortions while retaining a substantial unresolved direction-dependent systematic error.",
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        "title": "Precision Microwave Spectroscopy of the Positronium 2tripletS1 to2tripletP2 Interval (PRL131043001 archived formal copy)",
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        "description": "The free-space spectra diagnose field-dependent line shifts and do not provide a reliable precision interval. The redesigned experiment extrapolated finite-field measurements to zero field using a Zeeman model. Its two microwave directions differed by about 1.8 MHz; half this difference was assigned as an additional systematic uncertainty, rather than independently explained or eliminated. Mode simulations reproduced MHz shifts qualitatively but not the observed horn-angle dependence. Agreement with theory is limited to the reported uncertainty and does not resolve all earlier J=0 discrepancies. The cited archived paper and the later journal version differ in wording.",
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      "statement": "# Positronium microwave field diagnostics and fine-structure measurement with a redesigned apparatus\n\nSheldon and colleagues observed that the apparent positronium 2³S₁ → 2³P₂ transition frequency changed when a free-space microwave horn was rotated, even when the spectral lines showed little measurable asymmetry. They then measured the interval in a redesigned waveguide apparatus with reduced chamber reflections, reversed microwave directions and a retroreflected excitation laser. Averaging the two directions gave 8627.94±0.30(stat)±0.91(syst) MHz, within 1.3 standard deviations of the cited QED value. These experiments established practical diagnostics for microwave-field distortions while retaining a substantial unresolved direction-dependent systematic error.\n\n## Scientific scope\n\nThe free-space spectra diagnose field-dependent line shifts and do not provide a reliable precision interval. The redesigned experiment extrapolated finite-field measurements to zero field using a Zeeman model. Its two microwave directions differed by about 1.8 MHz; half this difference was assigned as an additional systematic uncertainty, rather than independently explained or eliminated. Mode simulations reproduced MHz shifts qualitatively but not the observed horn-angle dependence. Agreement with theory is limited to the reported uncertainty and does not resolve all earlier J=0 discrepancies. The cited archived paper and the later journal version differ in wording.\n\n## Reading status\n\nThis is a source-linked WRS catalogue note. A full explanatory guide and independent scientific reconstruction have not been completed for this entry. Read the identified original work for its complete narrative and arguments.\n\n## People and systems\n\nR. E. Sheldon; T. J. Babij; S. H. Reeder; S. D. Hogan; D. B. Cassidy\n\nThese are the listed authors of the cited contribution sources. Paper authorship does not quantify individual effort. An incomplete list is explicitly marked; same names are not automatically merged.\n\n\n\n## Original sources\n\n- [Microwave spectroscopy of positronium atoms in free space (PRA107042810)](https://discovery.ucl.ac.uk/id/eprint/10168858/1/PhysRevA.107.042810.pdf)\n- [Precision Microwave Spectroscopy of the Positronium 2tripletS1 to2tripletP2 Interval (PRL131043001 archived formal copy)](https://discovery.ucl.ac.uk/id/eprint/10174525/1/PhysRevLett.131.043001.pdf)\n",
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      "title": "Positronium microwave field diagnostics and fine-structure measurement with a redesigned apparatus"
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    "scope": "Sheldon and colleagues observed that the apparent positronium 2³S₁ → 2³P₂ transition frequency changed when a free-space microwave horn was rotated, even when the spectral lines showed little measurable asymmetry. They then measured the interval in a redesigned waveguide apparatus with reduced chamber reflections, reversed microwave directions and a retroreflected excitation laser. Averaging the two directions gave 8627.94±0.30(stat)±0.91(syst) MHz, within 1.3 standard deviations of the cited QED value. These experiments established practical diagnostics for microwave-field distortions while retaining a substantial unresolved direction-dependent systematic error. The free-space spectra diagnose field-dependent line shifts and do not provide a reliable precision interval. The redesigned experiment extrapolated finite-field measurements to zero field using a Zeeman model. Its two microwave directions differed by about 1.8 MHz; half this difference was assigned as an additional systematic uncertainty, rather than independently explained or eliminated. Mode simulations reproduced MHz shifts qualitatively but not the observed horn-angle dependence. Agreement with theory is limited to the reported uncertainty and does not resolve all earlier J=0 discrepancies. The cited archived paper and the later journal version differ in wording.",
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