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T Araki,
K Eguchi,
S Enomoto,
K Furuno,
K Ichimura,
H Ikeda,
K Inoue,
K Ishihara,
T Iwamoto,
T Kawashima, [......],
D M Markoff, J A Messimore,
K Nakamura,
R M Rohm,
W Tornow,
R Wendell,
A R Young,
M-J Chen,
Y-F Wang,
F Piquemal
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ABSTRACT: We present results of a study of neutrino oscillation based on a 766 ton/year exposure of KamLAND to reactor antineutrinos. We observe 258 nu (e) candidate events with energies above 3.4 MeV compared to 365.2+/-23.7 events expected in the absence of neutrino oscillation. Accounting for 17.8+/-7.3 expected background events, the statistical significance for reactor nu (e) disappearance is 99.998%. The observed energy spectrum disagrees with the expected spectral shape in the absence of neutrino oscillation at 99.6% significance and prefers the distortion expected from nu (e) oscillation effects. A two-neutrino oscillation analysis of the KamLAND data gives Deltam(2)=7.9(+0.6)(-0.5)x10(-5) eV(2). A global analysis of data from KamLAND and solar-neutrino experiments yields Deltam(2)=7.9(+0.6)(-0.5)x10(-5) eV(2) and tan((2)theta=0.40(+0.10)(-0.07), the most precise determination to date.
Physical Review Letters 04/2005; 94(8):081801. · 7.37 Impact Factor
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K Eguchi,
S Enomoto,
K Furuno,
H Ikeda,
K Ikeda,
K Inoue,
K Ishihara,
T Iwamoto,
T Kawashima,
Y Kishimoto, [......],
C R Gould,
H J Karwowski,
D M Markoff, J A Messimore,
K Nakamura,
R M Rohm,
W Tornow,
A R Young,
M-J Chen,
Y-F Wang
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ABSTRACT: Data corresponding to a KamLAND detector exposure of 0.28 kton yr has been used to search for nu;(e)'s in the energy range 8.3<E(nu;(e))<14.8 MeV. No candidates were found for an expected background of 1.1+/-0.4 events. This result can be used to obtain a limit on nu;(e) fluxes of any origin. Assuming that all nu;(e) flux has its origin in the Sun and has the characteristic 8B solar nu(e) energy spectrum, we obtain an upper limit of 3.7 x 10(2) cm(-2) s(-1) (90% C.L.) on the nu;(e) flux. We interpret this limit, corresponding to 2.8 x 10(-4) of the standard solar model 8B nu(e) flux, in the framework of spin-flavor precession and neutrino decay models.
Physical Review Letters 02/2004; 92(7):071301. · 7.37 Impact Factor
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K Eguchi,
S Enomoto,
K Furuno,
J Goldman,
H Hanada,
H Ikeda,
K Ikeda,
K Inoue,
K Ishihara,
W Itoh, [......],
L De Braeckeleer,
C R Gould,
H J Karwowski,
D M Markoff, J A Messimore,
K Nakamura,
R M Rohm,
W Tornow,
A R Young,
Y-F Wang
[show abstract]
[hide abstract]
ABSTRACT: KamLAND has measured the flux of nu;(e)'s from distant nuclear reactors. We find fewer nu;(e) events than expected from standard assumptions about nu;(e) propagation at the 99.95% C.L. In a 162 ton.yr exposure the ratio of the observed inverse beta-decay events to the expected number without nu;(e) disappearance is 0.611+/-0.085(stat)+/-0.041(syst) for nu;(e) energies >3.4 MeV. In the context of two-flavor neutrino oscillations with CPT invariance, all solutions to the solar neutrino problem except for the "large mixing angle" region are excluded.
Physical Review Letters 01/2003; 90(2):021802. · 7.37 Impact Factor
