	The latest results from the KamLAND
"Experimental investigation of geologically produced antineutrinos with KamLAND"

The KamLAND group has been observing neutrinos and antineutrinos since January, 2002 with the Kamioka liquid scintillator antineutrino detector (KamLAND), which is located in Kamioka Town, Hida City, Gifu Prefecture, Japan. In 2002 and 2004, results for neutrino oscillations using electron antineutrinos from nuclear reactors were reported. Using data collected through October, 2004, the KamLAND has detected electron antineutrinos produced by the decay of ²³⁸U and ²³²Th within the Earth, so-called geoneutrinos, for the first time. The number of geoneutrinos detected is consistent with the number predicted by a geophysical model. The radiogenic power from the decay of ²³⁸U and ²³²Th is essential to understand the dynamics, formation and evolution of the Earth. The measurement of geoneutrinos, produced by the heat source in the Earth, means we obtain a new method for the research on the deep inside of the Earth and a new window into “Neutrino Geophysics” is opened. These results were published in the July 28 issue of Nature magazine.
[Related links] Nature

[Large image(16KB)]	Electron antineutrino energy spectra in KamLAND Data points show energy distribution of 152 observed electron antineutrino candidates. Also shown are the expected signals from ²³⁸U (dot-dashed red line) and ²³²Th (dotted green line) geoneutrinos, and the total expected spectrum excluding the geoneutrino signal (thick solid black line) due to the backgrounds (dashed light blue line, dotted brown line and dashed purple line), and the total expectation (thin black line).

[Large image(11KB)]	Confidence intervals for the number of observed geoneutrinos Assuming the mass ratio, Th/U=3.9, the 90% confidence interval for the total number of ²³⁸U and ²³²Th geoneutrino candidates is estimated to be 4.5 to 54.2. The grey band shows the number of ²³⁸U and ²³²Th geoneutrinos predicted by the geophysical model. The KamLAND results are consistent with the prediction.

Collaboration links

Lawrence Berkeley National Laboratory/University of California,Berkeley

University of Hawaii

Stanford University

University of Tennessee

Last modified: 8/1/2005 3:01:48 PM JST