Reactor on-off antineutrino measurement with KamLAND

The recent long-term shutdown of Japanese nuclear reactors has resulted in a significantly reduced reactor {}₄ flux at KamLAND. This running condition provides a unique opportunity to confirm and constrain backgrounds for the reactor {}₄ oscillation analysis. The data set also has improved sensitivity for other {}₄ signals, in particular {}₄'s produced in -decays from ^238U and ^232Th within the Earth's interior, whose energy spectrum overlaps with that of reactor {}₄'s. Including constraints on 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^2₁₂=0. 436-₀. ₀₂₅^+0. 029, m₂₁^2=7. 53-₀. ₁₈^+0. 1810^-5 eV^2, and sin^2₁₃=0. 023-₀. ₀₀₂^+0. 002. Assuming a chondritic Th/U mass ratio, we obtain 116-₂₇^+28 {}₄ events from ^238U and ^232Th, corresponding to a geo {}₄ flux of 3. 4-₀. ₈^+0. 810^6 cm^-2 s^-1 at the KamLAND location. We evaluate various bulk silicate Earth composition models using the observed geo {}₄ rate.