The recent long-term shutdown of Japanese nuclear reactors has resulted in a significantly reduced reactor ν̄e flux at KamLAND. This running condition provides a unique opportunity to confirm and constrain backgrounds for the reactor ν̄e oscillation analysis. The data set also has improved sensitivity for other ν̄e signals, in particular ν̄e's produced in β-decays from U238 and Th232 within the Earth's interior, whose energy spectrum overlaps with that of reactor ν̄e's. Including constraints on θ13 from accelerator and short-baseline reactor neutrino experiments, a combined three-flavor analysis of solar and KamLAND data gives fit values for the oscillation parameters of tan2θ12=0.436-0.025+0.029, Δm212=7.53-0.18+0.18×10-5 eV2, and sin2θ13=0.023-0.002+0.002. Assuming a chondritic Th/U mass ratio, we obtain 116-27+28 ν̄e events from U238 and Th232, corresponding to a geo ν̄e flux of 3.4-0.8+0.8×106 cm-2 s-1 at the KamLAND location. We evaluate various bulk silicate Earth composition models using the observed geo ν̄e rate.
|ジャーナル||Physical Review D - Particles, Fields, Gravitation and Cosmology|
|出版ステータス||Published - 2013 8 2|
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