Antineutrino science in KamLAND

Abstract

The primary goal of KamLAND is a search for the oscillation of (Formula presented.)’s emitted from distant power reactors. The long baseline, typically 180 km, enables KamLAND to address the oscillation solution of the “solar neutrino problem” with (Formula presented.)’s under laboratory conditions. KamLAND found fewer reactor (Formula presented.) events than expected from standard assumptions about (Formula presented.) propagation at more than 9(Formula presented.) confidence level (C.L.). The observed energy spectrum disagrees with the expected spectral shape at more than 5(Formula presented.) C.L., and prefers the distortion from neutrino oscillation effects. A three-flavor oscillation analysis of the data from KamLAND and KamLAND + solar neutrino experiments with CPT invariance, yields (Formula presented.). All solutions to the solar neutrino problem except for the large mixing angle region are excluded. KamLAND also demonstrated almost two cycles of the periodic feature expected from neutrino oscillation effects. KamLAND performed the first experimental study of antineutrinos from the Earth’s interior so-called geoneutrinos (geo (Formula presented.)’s, and succeeded in detecting geo (Formula presented.) ’s produced by the decays of (Formula presented.) U and (Formula presented.) Th within the Earth. Assuming a chondritic Th/U mass ratio, we obtain (Formula presented.) events from (Formula presented.) U and (Formula presented.) Th, corresponding a geo (Formula presented.) flux of (Formula presented.) at the KamLAND location. We evaluate various bulk silicate Earth composition models using the observed geo (Formula presented.) rate.