Antineutrino science by KamLAND.
Bottom Line:
KamLAND measured the ν̄ e's flux from distant nuclear reactors, and found fewer events than expected from standard assumptions about ν̄ e propagation at the 99.998% confidence level (C.L.).The total observed number of 4.5 to 54.2, assuming a Th/U mass concentration ratio of 3.9 is consistent with 19 predicted by geophysical models.This detection allows better estimation of the abundances and distributions of radioactive elements in the Earth, and of the Earth's overall heat budget.
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Affiliation: Director General, High Energy Accelerator Research Organization, Ibaraki, Japan . ; Director General, High Energy Accelerator Research Organization, Ibaraki, Japan .
ABSTRACT
KamLAND measured the ν̄ e's flux from distant nuclear reactors, and found fewer events than expected from standard assumptions about ν̄ e propagation at the 99.998% confidence level (C.L.). The observed energy spectrum disagrees with the expected spectral shape at 99.6% C.L., and prefers the distortion from neutrino oscillation effects. A two-flavor oscillation analysis of the data from KamLAND and solar neutrino experiments with CPT invariance, yields [Formula: see text] eV(2) and [Formula: see text]. All solutions to the solar neutrino problem except for the large mixing angle (LMA) region are excluded. KamLAND succeeded in detecting geoneutrinos produced by the decays of (238)U and (232)Th within the Earth. The total observed number of 4.5 to 54.2, assuming a Th/U mass concentration ratio of 3.9 is consistent with 19 predicted by geophysical models. This detection allows better estimation of the abundances and distributions of radioactive elements in the Earth, and of the Earth's overall heat budget. No MeSH data available. Related in: MedlinePlus |
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Mentions: An un-binned maximum likelihood analysis of the ν̄e energy spectrum is carried out as a cross-check of extracting the number of geoneutrino events. Here the reactor neutrino oscillation parameters are allowed to take the values of the best-fit ±1σ. The confidence intervals for the number of geoneutrinos are shown in Fig. 14 (a). The best fit gives 3 238U and 18 232Th geoneutrinos shown by the dark circle. Although this result is somehow contradict with that of our reference Earth model indicated by the rectangular box in Fig. 14 (a), even 68.3% C.L. contour covers this box. Based on a study of chondritic meteorites, the Th/U mass ratio in the Earth is believed to be between 3.7 and 4.1, and is known better than either absolute concentration. Hence we investigate the χ2 behavior, assuming a Th/U ratio of 3.9, which corresponds to the χ2 distribution along the dotted line in Fig. 14 (a). With the 90% C.L. the total number of 238U and 232Th geoneutrinos are 4.5 to 54.2, as shown in Fig. 14 (b). The central value of 28.0 is consistent with 25 obtained the above rate-only analysis. The 99% confidence upper limit of the total 238U and 232Th geoneutrino flux at Kam-LAND is 1.62 × 107 cm−2s−1 which corresponds to an upper limit on radiogenic power of 60 TW for our reference Earth model. There is currently a program underway to reduce the 210Pb content of the detector. This should help to reduce the substantial systematic error due to the 13C(α, n)16O background. Further background reduction will require a new detector location, far away from nuclear reactors. The reported investigation of geoneutrinos should pave the way to future and more accurate measurements, which may provide a new window for the exploration of the Earth. |
View Article: PubMed Central - PubMed
Affiliation: Director General, High Energy Accelerator Research Organization, Ibaraki, Japan . ; Director General, High Energy Accelerator Research Organization, Ibaraki, Japan .
No MeSH data available.