Constraints on θ13 from a three-flavor oscillation analysis of reactor antineutrinos at KamLAND

We present new constraints on the neutrino oscillation parameters Delta m(21)(2), theta(12), and theta(13) 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 x 10(32) target-proton-year. Under the assumption of CPT invariance, a two-flavor analysis (theta(13) = 0) of the KamLAND and solar data yields the best-fit values tan(2)theta(12) = 0.444(-0.030)(+0.036) and Delta m(21)(2) = 7.50(-0.20)(+0.19) x 10(-5) eV(2); a three-flavor analysis with theta(13) as a free parameter yields the best-fit values tan(2)theta(12) = 0.452(-0.033)(+0.035), Delta m(21)(2) = 7.50(-0.20)(+0.19) x 10(-5) eV(2), and sin(2)theta(13) = 0.020(-0.016)(+0.016). This theta(13) interval is consistent with other recent work combining the CHOOZ, atmospheric and long-baseline accelerator experiments. We also present a new global theta(13) analysis, incorporating the CHOOZ, atmospheric, and accelerator data, which indicates sin(2)theta(13) = 0.009(-0.007)(+0.013). A nonzero value is suggested, but only at the 79% C.L.