Direct Observation of the Hyperfine Transition of the Ground State Positronium

Abstract

We report the first direct measurement of the hyperfine transition of the ground state positronium. The hyperfine structure between ortho-positronium and para-positronium is about 203 GHz. We develop a new optical system to accumulate about 10 kW power using a gyrotron, a mode converter, and a Fabry-Pérot cavity. The hyperfine transition has been observed with a significance of 5.4 standard deviations. The transition probability is measured to be $A=3.1_{-1.2}^{+1.6}\times 10^{-8}$ s${}^{-1}$ for the first time, which is in good agreement with the theoretical value of $3.37\times 10^{-8}$ s${}^{-1}$.

References in corpus (1)

• First test of $O({\alpha }^2)$ correction of the orthopositronium decay rate

Cited by in corpus (11)

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• Gyrotrons for High-Power Terahertz Science and Technology at FIR UF
• First Millimeter-wave Spectroscopy of the Ground-state Positronium
• Hyperfine splitting in positronium to $\mathcal{O}({\alpha }^7{m}_e)$: one-photon annihilation contribution
• Three-photon-annihilation contributions to positronium energies at order $m{\alpha }^7$
• Positronium hyperfine splitting at order $m{\alpha }^7$: light-by-light scattering in the two-photon-exchange channel
• Positronium energy levels at order $m{\alpha }^7$: light-by-light scattering in the two-photon-annihilation channel
• Positronium energy levels at order $m{\alpha }^7$: Product contributions in the two-photon-annihilation channel
• Annihilation energy and decay time of an ortho-Positronium