Reactor on-off antineutrino measurement with KamLAND
The recent long-term shutdown of Japanese nuclear reactors has resulted in a significantly reduced reactor ν ̄e flux at KamLAND. This running condition provides a unique opportunity to confirm and constrain backgrounds for the reactor ν ̄e oscillation analysis. The data set also has improved sensitivity for other ν ̄e signals, in particular ν ̄e 's produced in β-decays from U238 and Th232 within the Earth's interior, whose energy spectrum overlaps with that of reactor ν ̄e 's. Including constraints on θ 13 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 tan 2θ 12 =0.436-0.025+0.029, Δm212=7.53-0.18+0.18×10 - 5 eV2, and sin 2θ 13 =0.023-0.002+0.002. Assuming a chondritic Th/U mass ratio, we obtain 116-27+28 ν ̄e events from U238 and Th232, corresponding to a geo ν ̄e 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 ν ̄e rate. © 2013 American Physical Society.
Gando, A; Gando, Y; Hanakago, H; Ikeda, H; Inoue, K; Ishidoshiro, K; Ishikawa, H; Koga, M; Matsuda, R; Matsuda, S; Mitsui, T; Motoki, D; Nakamura, K; Obata, A; Oki, A; Oki, Y; Otani, M; Shimizu, I; Shirai, J; Suzuki, A; Takemoto, Y; Tamae, K; Ueshima, K; Watanabe, H; Xu, BD; Yamada, S; Yamauchi, Y; Yoshida, H; Kozlov, A; Yoshida, S; Piepke, A; Banks, TI; Fujikawa, BK; Han, K; O'Donnell, T; Berger, BE; Learned, JG; Matsuno, S; Sakai, M; Efremenko, Y; Karwowski, HJ; Markoff, DM; Tornow, W; Detwiler, JA; Enomoto, S; Decowski, MP
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