Enhanced Constraints on theta13 from A Three-Flavor Oscillation Analysis of Reactor Antineutrinos at KamLAND

• Published in: Physical review. D, Particles, fields, gravitation, and cosmology Particles, fields, gravitation, and cosmology, 2010-09
• Main Authors: The KamLAND Collaboration, Gando, A., Gando, Y., Ichimura, K., Ikeda, H., Inoue, K., Kibe, Y., Kishimoto, Y., Koga, M., Minekawa, Y., Mitsui, T., Morikawa, T., Nagai, N., Nakajima, K., Nakamura, K., Narita, K., Shimizu, I., Shimizu, Y., Shirai, J., Suekane, F., Suzuki, A., Takahashi, H., Takahashi, N., Takemoto, Y., Tamae, K., Watanabe, H., Xu, B. D., Yabumoto, H., Yoshida, H., Yoshida, S., Enomoto, S., Kozlov, A., Murayama, H., Grant, C., Keefer, G., Piepke, A., Banks, T. I., Bloxham, T., Detwiler, J. A., Freedman, S. J., Fujikawa, B. K., Han, K., Kadel, R., O'Donnell, T., Steiner, H. M., Dwyer, D. A., McKeown, R. D., Zhang, C., Berger, B. E., Lane, C. E., Maricic, J., Miletic, T., Batygov, M., Learned, J. G., Matsuno, S., Sakai, M., Horton-Smith, G. A., Downum, K. E., Gratta, G., Efremenko, Y., Perevozchikov, O., Karwowski, H. J., Markoff, D. M., Tornow, W., Heeger, K. M., Decowski, M. P.
• Format: Article
• Language: English
• Subjects: 72; 79; ACCELERATORS; ANTINEUTRINOS; NEUTRINO OSCILLATION; OSCILLATIONS
• ISSN: 1550-7998; 1550-2368

We present new constraints on the neutrino oscillation parameters {Delta}m{sub 21}{sup 2}, {theta}{sub 12}, and {theta}{sub 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{sup 32} target-proton-year. Under the assumption of CPT invariance, a two-flavor analysis ({theta}{sub 13} = 0) of the KamLAND and solar data yields the best-fit values tan{sup 2} {theta}{sub 12} = 0.444{sub -0.030}{sup +0.036} and {Delta}m{sub 21}{sup 2} = 7.50{sub -0.20}{sup +0.19} x 10{sup -5} eV{sup 2}; a three-flavor analysis with {theta}{sub 13} as a free parameter yields the best-fit values tan{sup 2} {theta}{sub 12} = 0.452{sub -0.033}{sup +0.035}, {Delta}m{sub 21}{sup 2} = 7.50{sub -0.20}{sup +0.19} x 10{sup -5}eV{sup 2}, and sin{sup 2} {theta}{sub 13} = 0.020{sub -0.016}{sup +0.016}. This {theta}{sub 13} interval is consistent with other recent work combining the CHOOZ, atmospheric and long-baseline accelerator experiments. We also present a new global {theta}{sub 13} analysis, incorporating the CHOOZ, atmospheric and accelerator data, which indicates sin{sup 2} {theta}{sub 13} = 0.017{sub -0.009}{sup +0.010}, a nonzero value at the 93% C.L. This finding will be further tested by upcoming accelerator and reactor experiments.