Precision Measurement of Neutrino Oscillation Parameters with KamLAND
A. Tang, E. Guardincerri, S. Yoshida, M. P. Decowski, Y. Kishimoto, T. Miletic, H. J. Karwowski, Y. Kamyshkov, D. McKee, K. Tamae, G. Gratta, J. Maricic, M. Nakamura, C. Jillings, Y. Kibe, T. Classen, Y. Shimizu, J. Shirai, Y. Efremenko, A. Kozlov, W. Bugg, K. Furuno, K. E. Downum, A. Terashima, D. A. Dwyer, H. Murayama, F. Piquemal, K. Owada, K. B. Luk, J. A. Detwiler, S. Enomoto, W. Tornow, G. A. Horton-Smith, P. Vogel, T. O'Donnell, J. G. Learned, F. Suekane, S. Matsuno, I. Shimizu, K. Tolich, F. Gray, D. S. Leonard, S. Abe, M. Koga, D. M. Markoff, C. Mauger, S. Dazeley, A. Piepke, E. Yonezawa, L. Hsu, C. Lane, K. Ichimura, H. Watanabe, Y. Gando, B. E. Berger, R. D. McKeown, J. Busenitz, L. A. Winslow, M. Batygov, O. Perevozchikov, C. Grant, Y. Minekawa, Ricol, J. S., S. J. Freedman, S. Pakvasa, H. Ikeda, K. Nakamura, A. Suzuki, C. Zhang, C. Lendvai, T. Ebihara, K. Inoue, R. Kadel, K. M. Heeger, B. K. Fujikawa, G. Keefer, Nakajima, K., Nakajima, K., T. Mitsui, Y. Takemoto, H. M. Steiner, J. Foster
Abstract
The KamLAND experiment has determined a precise value for the neutrino oscillation parameter $\Delta m^{2}_{21}$ and stringent constraints on $\theta_{12}$. The exposure to nuclear reactor anti-neutrinos is increased almost fourfold over previous results to 2.44$\times10^{32}$ proton-yr due to longer livetime and an enlarged fiducial volume. An undistorted reactor $\bar{\nu}_{e}$ energy spectrum is now rejected at >5$\sigma$. Extending the analysis down to the inverse beta decay energy threshold, and incorporating geo-neutrinos, gives a best-fit at $\Delta m^{2}_{21}$= $7.58^{+0.14}_{-0.13}(stat)^{+0.15}_{-0.15}(syst)\times10^{-5}$ eV$^{2}$ and $\tan^2 \theta_{12}$=$0.56^{+0.10}_{0.07}(stat)^{+0.10}_{-0.06}(syst)$. Local $\Delta \chi^2$-minima at higher and lower $\Delta m^{2}_{21}$ are disfavored at >4$\sigma$. Combining with solar neutrino data, we obtain $\Delta m^{2}_{21}$= $7.59^{+0.21}_{-0.21}\times10^{-5}$ eV$^{2}$ and $\tan^2 \theta_{12}$=$0.47^{+0.06}_{-0.05}$.