Search for n-n ¯ oscillation in Super-Kamiokande SEARCH FOR n-n ¯ OSCILLATION IN SUPER-⋯ K. ABE et al.

Author(s): Abe, K; Hayato, Y; Iida, T; Ishihara, K; Kameda, J; Koshio, Y; Minamino, A; Mitsuda, C; Miura, M; Moriyama, S; Nakahata, M; Obayashi, Y; Ogawa, H; Sekiya, H; Shiozawa, M; Suzuki, Y; Takeda, A; Takeuchi, Y; Ueshima, K; Watanabe, H; Higuchi, I; Ishihara, C; Ishitsuka, M; Kajita, T; Kaneyuki, K; Mitsuka, G; Nakayama, S; Nishino, H; Okumura, K; Saji, C; Takenaga, Y; Clark, S; Desai, S; Dufour, F; Herfurth, A; Kearns, E; Likhoded, S; Litos, M; Raaf, JL; Stone, JL; Sulak, LR; Wang, W; Goldhaber, M; Casper, D; Cravens, JP; Dunmore, J; Griskevich, J; Kropp, WR; Liu, DW; Mine, S; Regis, C; Smy, MB; Sobel, HW; Vagins, MR; Ganezer, KS; Hartfiel, B; Hill, J; Keig, WE; Jang, JS; Jeoung, IS; Kim, JY; Lim, IT; Scholberg, K; Tanimoto, N; Walter, CW; Wendell, R; Ellsworth, RW; Tasaka, S; Guillian, G; Learned, JG; Matsuno, S; Messier, MD; Ichikawa, AK; Ishida, T; Ishii, T; Iwashita, T; Kobayashi, T; Nakadaira, T; Nakamura, K; Nishikawa, K; Nitta, K; Oyama, Y; Suzuki, AT; Hasegawa, M; Maesaka, H | Abstract: A search for neutron-antineutron (n-n¯) oscillation was undertaken in Super-Kamiokande using the 1489 live-day or 2.45×1034 neutron-year exposure data. This process violates both baryon and baryon minus lepton numbers by an absolute value of two units and is predicted by a large class of hypothetical models where the seesaw mechanism is incorporated to explain the observed tiny neutrino masses and the matter-antimatter asymmetry in the Universe. No evidence for n-n¯ oscillation was found; the lower limit of the lifetime for neutrons bound in O16, in an analysis that included all of the significant sources of experimental uncertainties, was determined to be 1.9×1032years at the 90% confidence level. The corresponding lower limit for the oscillation time of free neutrons was calculated to be 2.7×108s using a theoretical value of the nuclear suppression factor of 0.517×1023s-1 and its uncertainty.