1. Research Center for Neutrino Science, Tohoku University, Sendai 980-8578, Japan
2. Department of Physics and Astronomy, University of Alabama, Tuscaloosa, Alabama 35487, USA
3. Physics Department, University of California at Berkeley and Lawrence Berkeley National Laboratory, Berkeley, California 94720, USA
4. W. K. Kellogg Radiation Laboratory, California Institute of Technology, Pasadena, California 91125, USA
5. Physics Department, Drexel University, Philadelphia, Pennsylvania 19104, USA
6. Department of Physics and Astronomy, University of Hawaii at Manoa, Honolulu, Hawaii 96822, USA
7. Department of Physics, Kansas State University, Manhattan, Kansas 66506, USA
8. Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803, USA
9. Physics Department, University of New Mexico, Albuquerque, New Mexico 87131, USA
10. Physics Department, Stanford University, Stanford, California 94305, USA
11. Department of Physics and Astronomy, University of Tennessee, Knoxville, Tennessee 37996, USA
12. Physics Department, Duke University, Durham, North Carolina 27008, USA, and Physics Department, North Carolina State, Raleigh, North Carolina 27695, USA, and Physics Department, University of North Carolina, Chapel Hill, North Carolina 27599, USA
13. Institute of High Energy Physics, Beijing 100039, China
14. CEN Bordeaux-Gradignan, IN2P3-CNRS and University Bordeaux I, F-33175 Gradignan Cedex, France

Correspondence to: S. Enomoto¹N. Tolich¹⁰ Correspondence and requests for materials should be addressed to S.E. (Email: sanshiro@awa.tohoku.ac.jp) or N.T. (Email: nrtolich@lbl.gov).

Abstract

The detection of electron antineutrinos produced by natural radioactivity in the Earth could yield important geophysical information. The Kamioka liquid scintillator antineutrino detector (KamLAND) has the sensitivity to detect electron antineutrinos produced by the decay of ²³⁸U and ²³²Th within the Earth. Earth composition models suggest that the radiogenic power from these isotope decays is 16 TW, approximately half of the total measured heat dissipation rate from the Earth. Here we present results from a search for geoneutrinos with KamLAND. Assuming a Th/U mass concentration ratio of 3.9, the 90 per cent confidence interval for the total number of geoneutrinos detected is 4.5 to 54.2. This result is consistent with the central value of 19 predicted by geophysical models. Although our present data have limited statistical power, they nevertheless provide by direct means an upper limit (60 TW) for the radiogenic power of U and Th in the Earth, a quantity that is currently poorly constrained.

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