Precision measurement of neutrino oscillation parameters with KamLAND

The KamLAND experiment has determined a precise value for the neutrino oscillation parameter Delta m(21)(2) and stringent constraints on theta(12). The exposure to nuclear reactor antineutrinos is increased almost fourfold over previous results to 2.44x10(32) proton yr due to longer livetime and an enlarged fiducial volume. An undistorted reactor (nu) over bar (e) energy spectrum is now rejected at > 5 sigma. Analysis of the reactor spectrum above the inverse beta decay energy threshold, and including geoneutrinos, gives a best fit at Delta m(21)(2)=7.58(-0.13)(+0.14)(stat)(-0.15)(+0.15)(syst) x 10(-5) eV(2) and tan(2)theta(12)=0.56(-0.07)(+0.10)(stat)(-0.06)(+0.10)(syst). Local Delta chi(2) minima at higher and lower Delta m(21)(2) are disfavored at > 4 sigma. Combining with solar neutrino data, we obtain Delta m(21)(2)=7.59(-0.21)(+0.21) x 10(-5) eV(2) and tan(2)theta(12)=0.47(-0.05)(+0.06).