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Register a new userPrecise measurement of HFS of positronium
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The ground state hyperfine splitting in positronium, $Delta _{mathrm{HFS}}$, is sensitive to high order corrections of QED. A new calculation up to $O(alpha ^3)$ has revealed a $3.9 sigma$ discrepancy between the QED prediction and the experimental results. This discrepancy might either be due to systematic problems in the previous experiments or to contributions beyond the Standard Model. We propose an experiment to measure $Delta_{mathrm{HFS}}$ employing new methods designed to remedy the systematic errors which may have affected the previous experiments. Our experiment will provide an independent check of the discrepancy. The measurement is in progress and a preliminary result of $Delta_{mathrm{HFS}} = 203.399 pm 0.029 mathrm{GHz} (143 mathrm{ppm})$ has been obtained. A measurement with a precision of O(1) ppm is expected within a few years.
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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 measurement of the two-neutrino double-beta ($2 ubetabeta$) decay of $^{100}$Mo to the ground state of $^{100}$Ru using lithium molybdate (crystal) scintillating bolometers. The detectors were developed for the CUPID-Mo program and operated at the EDELWEISS-III low background facility in the Modane underground laboratory. From a total exposure of $42.235$ kg$times$d, the half-life of $^{100}$Mo is determined to be $T_{1/2}^{2 u}=[7.12^{+0.18}_{-0.14},mathrm{(stat.)}pm0.10,mathrm{(syst.)}]times10^{18}$ years. This is the most accurate determination of the $2 ubetabeta$ half-life of $^{100}$Mo to date. We also confirm, with the statistical significance of $>3sigma$, that the single-state dominance model of the $2 ubetabeta$ decay of $^{100}$Mo is favored over the high-state dominance model.
Positronium is an ideal system for the research of the quantum electrodynamics (QED) in bound state. The hyperfine splitting (HFS) of positronium, $Delta_{mathrm{HFS}}$, gives a good test of the bound state calculations and probes new physics beyond the Standard Model. A new method of QED calculations has revealed the discrepancy by 15,ppm (3.9$sigma$) of $Delta_{mathrm{HFS}}$ between the QED prediction and the experimental average. There would be possibility of new physics or common systematic uncertainties in the previous all experiments. We describe a new experiment to reduce possible systematic uncertainties and will provide an independent check of the discrepancy. We are now taking data and the current result of $Delta_{mathrm{HFS}} = 203.395,1 pm 0.002,4 (mathrm{stat.}, 12,mathrm{ppm}) pm 0.001,9 (mathrm{sys.}, 9.5,mathrm{ppm}),mathrm{GHz} $ has been obtained so far. A measurement with a precision of $O$(ppm) is expected within a year.
We present a measurement of the geo--neutrino signal obtained from 1353 days of data with the Borexino detector at Laboratori Nazionali del Gran Sasso in Italy. With a fiducial exposure of (3.69 $pm$ 0.16) $times$ $10^{31}$ proton $times$ year after all selection cuts and background subtraction, we detected (14.3 $pm$ 4.4) geo-neutrino events assuming a fixed chondritic mass Th/U ratio of 3.9. This corresponds to a geo-neutrino signal $S_{geo}$ = (38.8 $pm$ 12.0) TNU with just a 6 $times$ $10^{-6}$ probability for a null geo-neutrino measurement. With U and Th left as free parameters in the fit, the relative signals are $S_{mathrm{Th}}$ = (10.6 $pm$ 12.7) TNU and $S_mathrm{U}$ = (26.5 $pm$ 19.5) TNU. Borexino data alone are compatible with a mantle geo--neutrino signal of (15.4 $pm$ 12.3) TNU, while a combined analysis with the KamLAND data allows to extract a mantle signal of (14.1 $pm$ 8.1) TNU. Our measurement of a reactor anti--neutrino signal $S_{react}$ = 84.5$^{+19.3}_{-18.9}$ TNU is in agreement with expectations in the presence of neutrino oscillations.
Positronium is a unique laboratory to study fundamental symmetries in the Standard Model, reflection in space ($mathcal{P}$), reversal in time ($mathcal{T}$), charge conjugation ($mathcal{C}$) and their combinations. The experimental limits on the $mathcal{C}$, $mathcal{CP}$ and $mathcal{CPT}$ symmetries violation in the decays of positronium are still several orders of magnitude higher than the expectations. The newly constructed Jagiellonian Positron Emission Tomograph (J-PET) was optimized for the registration of photons from the electron-positron annihilations. It enables tests of discrete symmetries in decays of positronium atoms via the determination of the expectation values of the discrete-symmetries-odd operators. In this article we present the capabilities of the J-PET detector in improving the current precision of discrete symmetries tests and report on the progress of analysis data from the first data-taking runs.
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