Measurement of neutrino oscillation by the K2K experiment

M. H. Ahn, E. Aliu, S. Andringa, S. Aoki, Y. Aoyama, J. Argyriades, K. Asakura, R. Ashie, F. Berghaus, H. G. Berns, H. Bhang, A. Blondel, S. Borghi, J. Bouchez, S. C. Boyd, J. Burguet-Castell, D. Casper, J. Catala, C. Cavata, A. CerveraS. M. Chen, K. O. Cho, J. H. Choi, U. Dore, S. Echigo, X. Espinal, M. Fechner, E. Fernandez, K. Fujii, Y. Fujii, S. Fukuda, Y. Fukuda, J. Gomez-Cadenas, R. Gran, T. Hara, M. Hasegawa, T. Hasegawa, K. Hayashi, Y. Hayato, R. L. Helmer, I. Higuchi, J. Hill, K. Hiraide, E. Hirose, J. Hosaka, A. K. Ichikawa, M. Ieiri, M. Iinuma, A. Ikeda, T. Inagaki

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651 Scopus citations


We present measurements of νμ disappearance in K2K, the KEK to Kamioka long-baseline neutrino oscillation experiment. One-hundred and twelve beam-originated neutrino events are observed in the fiducial volume of Super-Kamiokande with an expectation of 158.1-8.6+9.2 events without oscillation. A distortion of the energy spectrum is also seen in 58 single-ring muonlike events with reconstructed energies. The probability that the observations are explained by the expectation for no neutrino oscillation is 0.0015% (4.3σ). In a two-flavor oscillation scenario, the allowed Δm2 region at sin 22θ=1 is between 1.9 and 3.5×10-3eV2 at the 90% C.L. with a best-fit value of 2.8×10-3eV2.

Original languageEnglish (US)
Article number072003
JournalPhysical Review D - Particles, Fields, Gravitation and Cosmology
Issue number7
StatePublished - 2006

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