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Title: Positronium $2^3\mathrm{S}_1$ to $2^3\mathrm{P}_0$ interval disagrees with QED
Plain: Positronium, an electron bound to its antiparticle, tests quantum electrodynamics (QED, the quantum theory of light and charges) with no proton involved. One of its microwave transitions came out 4.5 standard errors away from theory.
Precise: The UCL measurement of the positronium $2^3S_1$ to $2^3P_0$ interval gave $18501.02(61)\,\mathrm{MHz}$ versus the QED prediction $18498.25(8)\,\mathrm{MHz}$ (Gurung et al 2020), a $4.5\,\sigma$ difference; later work by the same group traced line-shape distortions in related intervals to microwave reflections, but the $2^3P_0$ tension has not been removed. Determine whether the $2^3P_0$ discrepancy survives an independent method such as Ramsey separated-field spectroscopy.
Settled by: An independent $2^{3}\mathrm{S}_{1}$ to $2^{3}\mathrm{P}_{0}$ measurement at sub-0.3 MHz uncertainty with a different microwave geometry.
Kind: well-posed
Answer type: yes-no
References: (empty)
Literature status: open
Status note: (empty)
Posed since: 2020