Search for CP-violation in Positronium Decay

CP-violation in the quark sector has been well established over the last decade, but has not been observed in the lepton sector. We search for CP-violating decay processes in positronium, using the angular correlation of (\vec{S}\cdot\vec{k_{1}})(\vec{S}\cdot\vec{k_{1}}\times\vec{k_{2}}), where \vec{S} is the the positronium spin and \vec{k_{1}}, \vec{k_{2}} are the directions of the positronium decay photons. To a sensitivity of 2.2\times10^{-3}, no CP-violation has been found, which is at the level of the CP-violation amplitude in the K meson. A 90% confidence interval of the CP-violation parameter (C_{CP}) was determined to be -0.0023 < C_{CP} < 0.0049. This result is a factor 7 more strict than that of the previous experiment

Factors influencing the start of development in Daphnia pulex winter eggs [Translation from: Biological Reviews Vol. 13, 24-26, 1951]

The winter eggs of Daphnia pulex, after passing safely through the winter , develop and hatch in the spring, multiplying by themselves, while some males emerging among them with the changes in environment produce fertile eggs, which are universally known as winter eggs . This study researches the factors governing the development of winter eggs through experiments

Precision Measurement of Orthopositronium Decay Rate Using SiO_2 Powder

The intrinsic decay rate of orthopositronium formed in ${\rm SiO_2}$ powder is measured using the direct $2\gamma$ correction method such that the time dependence of the pick-off annihilation rate is precisely determined using high energy-resolution germanium detectors. As a systematic test, two different types of ${\rm SiO_2}$ powder are used with consistent findings. The intrinsic decay rate of orthopositronium is found to be $7.0396\pm0.0012 (stat.)\pm0.0011 (sys.)\mu s^{-1}$, which is consistent with previous measurements using ${\rm SiO_2}$ powder with about twice the accuracy. Results agree well with a recent $O(\alpha^2)$ QED prediction, varying $3.8-5.6$ experimental standard deviations from other measurements.Comment: 16 pages, 7 figures included. To be published in Physics Letters

Solution of Orthopositronium lifetime Puzzle

The intrinsic decay rate of orthopositronium formed in ${\rm SiO_2}$ powder is measured using the direct $2\gamma$ correction method such that the time dependence of the pick-off annihilation rate is precisely determined. The decay rate of orthopositronium is found to be $7.0396\pm0.0012 (stat.)\pm0.0011 (sys.)\mu s^{-1}$, which is consistent with our previous measurements with about twice the accuracy. Results agree well with the $O(\alpha^2)$ QED prediction, and also with a result reported very recently using nanoporous film

Results of a Search for Paraphotons with Intense X-ray Beams at SPring-8

A search for paraphotons, or hidden U(1) gauge bosons, is performed using an intense X-ray beamline at SPring--8. "Light Shining through a Wall" technique is used in this search. No excess of events above background is observed. A stringent constraint is obtained on the photon--paraphoton mixing angle, $\chi < 8.06\times 10^{-5}\ (95$ for $0.04\ {\rm eV}<m_{\gamma^{\prime}} < 26\ {\rm keV}$.Comment: 10 pages, 4 figure

Direct Observation of the Hyperfine Transition of the Ground State Positronium

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$^{-1}$