8,164 research outputs found

    Search for CP-violation in Positronium Decay

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    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]

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    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

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    The intrinsic decay rate of orthopositronium formed in SiO2{\rm SiO_2} powder is measured using the direct 2γ2\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 SiO2{\rm SiO_2} powder are used with consistent findings. The intrinsic decay rate of orthopositronium is found to be 7.0396±0.0012(stat.)±0.0011(sys.)μs−17.0396\pm0.0012 (stat.)\pm0.0011 (sys.)\mu s^{-1}, which is consistent with previous measurements using SiO2{\rm SiO_2} powder with about twice the accuracy. Results agree well with a recent O(α2)O(\alpha^2) QED prediction, varying 3.8−5.63.8-5.6 experimental standard deviations from other measurements.Comment: 16 pages, 7 figures included. To be published in Physics Letters

    Solution of Orthopositronium lifetime Puzzle

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    The intrinsic decay rate of orthopositronium formed in SiO2{\rm SiO_2} powder is measured using the direct 2γ2\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±0.0012(stat.)±0.0011(sys.)μs−17.0396\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(α2)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

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    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, χ<8.06×10−5 (95\chi < 8.06\times 10^{-5}\ (95%\ {\rm C.L.}) for 0.04 eV<mγ′<26 keV0.04\ {\rm eV}<m_{\gamma^{\prime}} < 26\ {\rm keV}.Comment: 10 pages, 4 figure

    Direct Observation of the Hyperfine Transition of the Ground State Positronium

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    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=3.1−1.2+1.6×10−8A = 3.1^{+1.6}_{-1.2} \times 10^{-8} s−1^{-1} for the first time, which is in good agreement with the theoretical value of 3.37×10−83.37 \times 10^{-8} s−1^{-1}
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