Constraints on ${\theta }_{13}$ from A Three-Flavor Oscillation Analysis of Reactor Antineutrinos at KamLAND

We present new constraints on the neutrino oscillation parameters $/textyen Delta m^{2}{21}$,$/textyen theta{12}$,and$/textyen theta_{13}$ 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 $3.49\text{textyen}times{10}^{32}$ target-proton-year. Under the assumption of {\textyen it CPT} invariance, a two-flavor analysis (/textyen mbox{$\textyen theta_{13} = 0}) of the KamLAND and solar data yields the best-fit values\textyen tan^{2} \textyen theta_{12} = 0.444^{+0.036}{-0.030}$and$\textyen Delta m^{2}{21} = 7.50^{+0.19}{-0.20} \textyen times 10^{-5} ~ {\textyen rm eV}^{2}$;athree-flavoranalysiswith$\textyen theta{13}$ as a free parameter yields the best-fit values $\textyen tan^{2} \textyen theta_{12} = 0.452^{+0.035}{-0.033}$,$\textyen Delta m^{2}{21} = 7.50^{+0.19}{-0.20} \textyen times 10^{-5} ~ {\textyen rm eV}^{2}$,and$\textyen sin^{2} \textyen theta{13} = 0.020^{+0.016}{-0.016}$\mathrm{.}This$\textyen theta{13}$ interval is consistent with other recent work combining the CHOOZ, atmospheric and long-baseline accelerator experiments. We also present a new global $\textyen theta_{13}$ analysis, incorporating the CHOOZ, atmospheric and accelerator data, which indicates $\textyen sin^{2} \textyen theta_{13} = 0.009^{+0.013}_{-0.007}$. A nonzero value is suggested, but only at the 79\textyen% C.L.