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Register a new userFirst direct measurement of positronium hyperfine splitting with sub-THz light
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Positronium is an ideal system for the research of the bound state QED. The hyperfine splitting of positronium (Ps-HFS, about 203 GHz) is an important observable but all previous measurements of Ps-HFS had been measured indirectly using Zeeman splitting. There might be the unknown systematic errors on the uniformity of magnetic field. We are trying to measure Ps-HFS directly using sub-THz radiation. We developed an optical system to accumulate high power (about 10 kW) radiation in a Fabry-Perot resonant cavity and observed the positronium hyperfine transition for the first time.
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Hyperfine splitting of positronium is an important parameter for particle physics. This paper gives experimental techniques and results of R&D studies of our experiment to observe direct hyperfine transition of ortho-positronium to para-positronium.
Positronium is an ideal system for the research of the QED, especially for the QED in bound state. The discrepancy of 3.9sigma is found recently between the measured HFS values and the QED prediction ($O(alpha^3)$). It might be due to the contribution of the unknown new physics or the systematic problems in the previous all measurements. We propose new method to measure HFS precisely and directly. A gyrotron, a novel sub-THz light source is used with a high-finesse Fabry-Perot cavity to obtain enough radiation power at 203 GHz. The present status of the optimization studies and current design of the experiment are described.
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-P{e}rot cavity. The hyperfine transition has been observed with a significance of 5.4 standard deviations. The transition probability is measured to be $A = 3.1^{+1.6}_{-1.2} times 10^{-8}$ s$^{-1}$ for the first time, which is in good agreement with the theoretical value of $3.37 times 10^{-8}$ s$^{-1}$.
Interference between different energy eigenstates in a quantum system results in an oscillation with a frequency which is proportional to the difference in energy between the states. Such an oscillation is observable in polarized positronium when it is placed in a magnetic field. In order to measure the hyperfine splitting of positronium, we perform the precise measurement of this oscillation using a high quality superconducting magnet and fast photon-detectors. A result of $203.324 pm 0.039rm{~(stat.)} pm 0.015rm{(~sys.)}$~GHz is obtained which is consistent with both theoretical calculations and previous precise measurements.
We report the results of the second measurement campaign of the Karlsruhe Tritium Neutrino (KATRIN) experiment. KATRIN probes the effective electron anti-neutrino mass, $m_{ u}$, via a high-precision measurement of the tritium $beta$-decay spectrum close to its endpoint at $18.6,mathrm{keV}$. In the second physics run presented here, the source activity was increased by a factor of 3.8 and the background was reduced by $25,%$ with respect to the first campaign. A sensitivity on $m_{ u}$ of $0.7,mathrm{eV/c^2}$ at $90,%$ confidence level (CL) was reached. This is the first sub-eV sensitivity from a direct neutrino-mass experiment. The best fit to the spectral data yields $m_{ u}^2 = (0.26pm0.34),mathrm{eV^4/c^4}$, resulting in an upper limit of $m_{ u}<0.9,mathrm{eV/c^2}$ ($90,%$ CL). By combining this result with the first neutrino mass campaign, we find an upper limit of $m_{ u}<0.8,mathrm{eV/c^2}$ ($90,%$ CL).
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