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تسجيل مستخدم جديدKamLAND, terrestrial heat sources and neutrino oscillations
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We comment on the first indication of geo-neutrino events from KamLAND and on the prospects for understanding Earth energetics. Practically all models of terrestrial heat production are consistent with data within the presently limited statistics, the fully radiogenic model being closer to the observed value ($approx 9$ geo-events). In a few years KamLAND should collect sufficient data for a clear evidence of geo-neutrinos, however discrimination among models requires a detector with the class and size of KamLAND far away from nuclear reactors. We also remark that the event ratio from Thorium and Uranium decay chains is well fixed $N(Th)/N(U) simeq 0.25$, a constraint that can be useful for determining neutrino oscillation parameters. We show that a full spectral analysis, including this constraint, further reduces the oscillation parameter space compared to an analysis with an energy threshold $E_{vis}>2.6 MeV$.
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We find that recent results from the KamLAND collaboration on geologically produced antineutrinos, N(U+Th) = 28+16-15 events, correspond to a radiogenic heat production from Uranium and Thorium decay chains H(U+Th) = 38+35-33 TW. The 99% confidence l
imit on the geo-neutrino signal translates into the upper bound H(U+Th) < 162 TW, which is much weaker than that claimed by KamLAND, H(U+Th) < 60 TW, based on a too narrow class of geological models. We also performed an analysis of KamLAND data including recent high precision measurements of the C13(alpha,n)O16 cross section. The result, N(U+Th) = 31+14-13, corroborates the evidence (approx 2.5sigma) for geo-neutrinos in KamLAND data.
We report a measurement of the neutrino-electron elastic scattering rate of 862 keV 7Be solar neutrinos based on a 165.4 kton-day exposure of KamLAND. The observed rate is 582 +/- 90 (kton-day)^-1, which corresponds to a 862 keV 7Be solar neutrino fl
ux of (3.26 +/- 0.50) x 10^9 cm^-2s^-1, assuming a pure electron flavor flux. Comparing this flux with the standard solar model prediction and further assuming three flavor mixing, a nu_e survival probability of 0.66 +/- 0.14 is determined from the KamLAND data. Utilizing a global three flavor oscillation analysis, we obtain a total 7Be solar neutrino flux of (5.82 +/- 0.98) x 10^9 cm^-2s^-1, which is consistent with the standard solar model predictions.
At the previous Venice meeting NO-VE 2008, we discussed possible hints in favor of a nonzero value for the unknown neutrino mixing angle theta(13), emerging from the combination of solar and long-baseline reactor data, as well as from the combination
of atmospheric, CHOOZ and long-baseline accelerator nu_mu->nu_mu data. Recent MINOS 2009 results in the nu_mu->nu_e appearance channel also seem to support such hints. A combination of all current oscillation data provides, as preferred range, sin^2 theta(13) = 0.02 +- 0.01 (1sigma). We review several issues raised by such hints in the last year, and comment on their possible near-future improvements and tests.
The KamLAND and Borexino experiments have detected electron antineutrinos produced in the decay chains of natural thorium and uranium (Th and U geoneutrinos). We analyze the energy spectra of current geoneutrino data in combination with solar and lon
g-baseline reactor neutrino data, with marginalized three-neutrino oscillation parameters. We consider the case with unconstrained Th and U event rates in KamLAND and Borexino, as well as cases with fewer degrees of freedom, as obtained by successively assuming for both experiments a common Th/U ratio, a common scaling of Th+U event rates, and a chondritic Th/U value. In combination, KamLAND and Borexino can reject the null hypothesis (no geoneutrino signal) at 5 sigma. Interesting bounds or indications emerge on the Th+U geoneutrino rates and on the Th/U ratio, in broad agreement with typical Earth model expectations. Conversely, the results disfavor the hypothesis of a georeactor in the Earths core, if its power exceeds a few TW. The interplay of KamLAND and Borexino geoneutrino data is highlighted.
The first results from the KamLAND experiment have provided confirmational evidence for the Large Mixing Angle (LMA) MSW solution to the solar neutrino problem. We do a global analysis of solar and the recently announced KamLAND data (both rate and s
pectrum) and investigate its effect on the allowed region in the $Delta m^2-tan^2theta$ plane. The best-fit from a combined analysis which uses the KamLAND rate plus global solar data comes at $Delta m^2 = 6.06 times 10^{-5}$ eV $^2$ and $tan^2theta=0.42$, very close to the global solar best-fit, leaving a large allowed region within the global solar LMA contour. The inclusion of the KamLAND spectral data in the global fit gives a best-fit $Delta m^2 = 7.15 times 10^{-5}$ eV $^2$ and $tan^2theta=0.42$ and constrains the allowed areas within LMA, leaving essentially two allowed zones. Maximal mixing though allowed by the KamLAND data alone is disfavored by the global solar data and remains disallowed at about $3sigma$. The LOW solution is now ruled out at about 5$sigma$ w.r.t. the LMA solution.
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