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- TL;DR Summary
- A recent study measures a transition frequency in positronium higher than predicted.
Precision Microwave Spectroscopy of the Positronium n=2 Fine Structure
A nice compact abstract, so I'll just quote it here:
The 0.61 MHz experimental uncertainty are the sum of 0.57 MHz statistical uncertainty, 0.215 MHz laser alignment and <0.1 MHz other sources.
The uncertainty on the 2.77 MHz difference is dominated by the statistical uncertainty and the significance is 4.5 standard deviations.
They produce very slow positronium excited by a laser, that suppresses uncertainties previous measurements had and improves the statistics. They also have ideas how to reduce the uncertainties that are still relevant. No indication of the measurement time that went into the study, but taking data for a longer time will certainly help even if they don't make larger upgrades.
A nice compact abstract, so I'll just quote it here:
Positronium with its two light leptons is the dream of every theorist, that keeps the uncertainties small.We report a new measurement of the positronium (Ps) 23S1→23P0 interval. Slow Ps atoms, optically excited to the radiatively metastable 23S1 level, flew through a microwave radiation field tuned to drive the transition to the short-lived 23P0 level, which was detected via the time spectrum of subsequent ground state Ps annihilation radiation. After accounting for Zeeman shifts we obtain a transition frequency ν0=18501.02±0.61 MHz, which is not in agreement with the theoretical value of ν0=18498.25±0.08 MHz.
The 0.61 MHz experimental uncertainty are the sum of 0.57 MHz statistical uncertainty, 0.215 MHz laser alignment and <0.1 MHz other sources.
The uncertainty on the 2.77 MHz difference is dominated by the statistical uncertainty and the significance is 4.5 standard deviations.
They produce very slow positronium excited by a laser, that suppresses uncertainties previous measurements had and improves the statistics. They also have ideas how to reduce the uncertainties that are still relevant. No indication of the measurement time that went into the study, but taking data for a longer time will certainly help even if they don't make larger upgrades.