Constraints on theta 13 from a three-flavor oscillation analysis of reactor antineutrinos at KamLAND

We present new constraints on the neutrino oscillation parameters Δm212, θ12, and θ13 from a three-flavor analysis of solar and KamLAND data. The KamLAND data set includes data acquired following a radiopurity upgrade and amounts to a total exposure of 3.49×1032 target-proton-year. Under the assumption of CPT invariance, a two-flavor analysis (θ13=0) of the KamLAND and solar data yields the best-fit values tan⁡2θ12=0.444-0.030+0.036 and Δm212=7.50-0.20+0.19×10-5  eV2; a three-flavor analysis with θ13 as a free parameter yields the best-fit values tan⁡2θ12=0.452-0.033+0.035, Δm212=7.50-0.20+0.19×10-5  eV2, and sin⁡2θ13=0.020-0.016+0.016. This θ13 interval is consistent with other recent work combining the CHOOZ, atmospheric and long-baseline accelerator experiments. We also present a new global θ13 analysis, incorporating the CHOOZ, atmospheric, and accelerator data, which indicates sin⁡2θ13=0.009-0.007+0.013. A nonzero value is suggested, but only at the 79% C.L.