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Title: Reactor- and Geo-Neutrino Detections from KamLAND

Abstract

Based on 766 ton-year exposure, the reactor anti-neutrino disappearance was reconfirmed with 99.998% C.L. and the observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance. These results prefer the {nu}-bare oscillation effects. In the context of the {nu}-bare {yields} {nu}-barx oscillation with CPT invariance, the combined analysis of data from KamLAND and solar neutrino experiments yields {delta}m{sup 2} = 7.9{sub -0.5}{sup +0.6} x 10{sup -5} eV{sup 2} and tan{sup 2} {theta} = 0.40{sub -0.07}{sup +0.10}. KamLAND has recently succeeded in detecting geo-neutrinos, {nu}-bares produced by natural radioactivity in the Earth. The present measurement is consistent with current geophysical models and constraints the {nu}-bare flux from U and Th in the planet to be less than 1.62 x 107 cm-2s-1 at 99% C.L.

Authors:
 [1]
  1. Research Center for Neutrino Science, Tohoku University, Aramaki, Aoba, Sendai, 980-8578 (Japan)
Publication Date:
OSTI Identifier:
20798039
Resource Type:
Journal Article
Resource Relation:
Journal Name: AIP Conference Proceedings; Journal Volume: 815; Journal Issue: 1; Conference: 25. international conference on physics in collision, Prague (Czech Republic), 5-9 Jul 2005; Other Information: DOI: 10.1063/1.2173572; (c) 2006 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
72 PHYSICS OF ELEMENTARY PARTICLES AND FIELDS; CPT THEOREM; DATA ANALYSIS; ENERGY SPECTRA; GEOPHYSICS; NATURAL RADIOACTIVITY; NEUTRINO DETECTION; NEUTRINO OSCILLATION; NEUTRINO REACTIONS; SOLAR NEUTRINOS

Citation Formats

Suzuki, Atsuto. Reactor- and Geo-Neutrino Detections from KamLAND. United States: N. p., 2006. Web. doi:10.1063/1.2173572.
Suzuki, Atsuto. Reactor- and Geo-Neutrino Detections from KamLAND. United States. doi:10.1063/1.2173572.
Suzuki, Atsuto. Wed . "Reactor- and Geo-Neutrino Detections from KamLAND". United States. doi:10.1063/1.2173572.
@article{osti_20798039,
title = {Reactor- and Geo-Neutrino Detections from KamLAND},
author = {Suzuki, Atsuto},
abstractNote = {Based on 766 ton-year exposure, the reactor anti-neutrino disappearance was reconfirmed with 99.998% C.L. and the observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance. These results prefer the {nu}-bare oscillation effects. In the context of the {nu}-bare {yields} {nu}-barx oscillation with CPT invariance, the combined analysis of data from KamLAND and solar neutrino experiments yields {delta}m{sup 2} = 7.9{sub -0.5}{sup +0.6} x 10{sup -5} eV{sup 2} and tan{sup 2} {theta} = 0.40{sub -0.07}{sup +0.10}. KamLAND has recently succeeded in detecting geo-neutrinos, {nu}-bares produced by natural radioactivity in the Earth. The present measurement is consistent with current geophysical models and constraints the {nu}-bare flux from U and Th in the planet to be less than 1.62 x 107 cm-2s-1 at 99% C.L.},
doi = {10.1063/1.2173572},
journal = {AIP Conference Proceedings},
number = 1,
volume = 815,
place = {United States},
year = {Wed Feb 08 00:00:00 EST 2006},
month = {Wed Feb 08 00:00:00 EST 2006}
}
  • No abstract prepared.
  • We present the results of a Bayesian analysis of solar and KamLAND neutrino data in the framework of three-neutrino mixing. We adopt two approaches for the prior probability distribution of the oscillation parameters {delta}m{sub 21}{sup 2}, sin{sup 2}{theta}{sub 12}, sin{sup 2}{theta}{sub 13}: (1) a traditional flat uninformative prior; and (2) an informative prior which describes the limits on sin{sup 2}{theta}{sub 13} obtained in atmospheric and long-baseline accelerator and reactor neutrino experiments. In both approaches, we present the allowed regions in the sin{sup 2}{theta}{sub 13}-{delta}m{sub 21}{sup 2} and sin{sup 2}{theta}{sub 12}-sin{sup 2}{theta}{sub 13} planes, as well as the marginal posterior probabilitymore » distribution of sin{sup 2}{theta}{sub 13}. We confirm the 1.2{sigma} hint of {theta}{sub 13}>0 found in [G. Fogli et al., Phys. Rev. Lett. 101, 141801 (2008).] from the analysis of solar and KamLAND neutrino data. We found that the statistical significance of the hint is reduced to about 0.8{sigma} by the constraints on sin{sup 2}{theta}{sub 13} coming from atmospheric and long-baseline accelerator and reactor neutrino data, in agreement with [T. Schwetz, M. Tortola, and J. W. F. Valle, New J. Phys. 10, 113011 (2008).].« less
  • 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 long-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 canmore » 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 Earth's core, if its power exceeds a few TW. The interplay of KamLAND and Borexino geoneutrino data is highlighted.« less
  • Radioactive isotopes inside the Earth produce geo-neutrinos through beta decays. Geo-neutrinos could be direct probes to investigate the interior of the Earth as a supplement to the current geophysical survey that mainly relies on an indirect seismic approach. After the Kamioka liquid scintillator antineutrino detector (KamLAND) reported the first indication of geo-neutrinos in 2005, we have accumulated data for a total of 2,135 days of live-time and achieved a lower background level by purifying liquid scintillator. The number of obtained geo-neutrino events is 106{sub -28}{sup +29} corresponding to an electron antineutrino flux of 4.3{sub -1.1}{sup +1.2}x10{sup 6} cm{sup -2} s{supmore » -1} from {sup 238}U and {sup 232}Th series at the Earth's surface. The null hypothesis for the existence of geo-neutrinos is excluded at the 99.997% confidence level. We combined this precise result with that of the Borexino experiment to obtain 20.0{sub -8.6}{sup +8.8} TW as a contribution of {sup 238}U and {sup 232}Th to the Earth heat flow.« less
  • We present new constraints on the neutrino oscillation parameters {Delta}m{sub 21}{sup 2}, {theta}{sub 12}, and {theta}{sub 13} from a three-flavor analysis of solar and KamLAND data. The KamLAND data set includes data acquired following a radiopurity upgrade and amounts to a total exposure of 3.49 x 10{sup 32} target-proton-year. Under the assumption of CPT invariance, a two-flavor analysis ({theta}{sub 13} = 0) of the KamLAND and solar data yields the best-fit values tan{sup 2} {theta}{sub 12} = 0.444{sub -0.030}{sup +0.036} and {Delta}m{sub 21}{sup 2} = 7.50{sub -0.20}{sup +0.19} x 10{sup -5} eV{sup 2}; a three-flavor analysis with {theta}{sub 13} asmore » a free parameter yields the best-fit values tan{sup 2} {theta}{sub 12} = 0.452{sub -0.033}{sup +0.035}, {Delta}m{sub 21}{sup 2} = 7.50{sub -0.20}{sup +0.19} x 10{sup -5}eV{sup 2}, and sin{sup 2} {theta}{sub 13} = 0.020{sub -0.016}{sup +0.016}. This {theta}{sub 13} interval is consistent with other recent work combining the CHOOZ, atmospheric and long-baseline accelerator experiments. We also present a new global {theta}{sub 13} analysis, incorporating the CHOOZ, atmospheric and accelerator data, which indicates sin{sup 2} {theta}{sub 13} = 0.017{sub -0.009}{sup +0.010}, a nonzero value at the 93% C.L. This finding will be further tested by upcoming accelerator and reactor experiments.« less