APS » Phys. Rev. D » Volume 77 » Issue 3

S. Mine,⁴ J. L. Alcaraz,¹ S. Andringa,¹ S. Aoki,¹⁴ J. Argyriades,⁵ K. Asakura,¹⁴ R. Ashie,²⁹ F. Berghaus,³ H. Berns,³³ H. Bhang,²⁴ A. Blondel,⁹ S. Borghi,⁹ J. Bouchez,⁵ J. Burguet-Castell,³² D. Casper,⁴ J. Catala,³² C. Cavata,⁵ A. Cervera,⁹ S. M. Chen,³¹ K. O. Cho,⁶ J. H. Choi,⁶ U. Dore,²³ X. Espinal,¹ M. Fechner,⁵ E. Fernandez,¹ Y. Fujii,¹¹ Y. Fukuda,¹⁹ J. Gomez-Cadenas,³² R. Gran,³³ T. Hara,¹⁴ M. Hasegawa,¹⁶ T. Hasegawa,¹¹ Y. Hayato,²⁹ R. L. Helmer,³¹ K. Hiraide,¹⁶ J. Hosaka,²⁹ A. K. Ichikawa,¹⁶ M. Iinuma,¹² A. Ikeda,²¹ T. Ishida,¹¹ K. Ishihara,²⁹ T. Ishii,¹¹ M. Ishitsuka,³⁰ Y. Itow,²⁹ T. Iwashita,¹¹ H. I. Jang,⁶ E. J. Jeon,²⁴ I. S. Jeong,⁶ K. K. Joo,²⁴ G. Jover,¹ C. K. Jung,²⁷ T. Kajita,³⁰ J. Kameda,²⁹ K. Kaneyuki,³⁰ I. Kato,³¹ E. Kearns,² C. O. Kim,¹⁵ M. Khabibullin,¹³ A. Khotjantsev,¹³ D. Kielczewska,^34,25 J. Y. Kim,⁶ S. B. Kim,²⁴ P. Kitching,³¹ K. Kobayashi,²⁷ T. Kobayashi,¹¹ A. Konaka,³¹ Y. Koshio,²⁹ W. Kropp,⁴ Yu. Kudenko,¹³ Y. Kuno,²² Y. Kurimoto,¹⁶ T. Kutter,^17,3 J. Learned,¹⁰ S. Likhoded,² I. T. Lim,⁶ P. F. Loverre,²³ L. Ludovici,²³ H. Maesaka,¹⁶ J. Mallet,⁵ C. Mariani,²³ S. Matsuno,¹⁰ V. Matveev,¹³ K. McConnel,¹⁸ C. McGrew,²⁷ S. Mikheyev,¹³ A. Minamino,²⁹ O. Mineev,¹³ C. Mitsuda,²⁹ M. Miura,²⁹ Y. Moriguchi,¹⁴ S. Moriyama,²⁹ T. Nakadaira,¹¹ M. Nakahata,²⁹ K. Nakamura,¹¹ I. Nakano,²¹ T. Nakaya,¹⁶ S. Nakayama,³⁰ T. Namba,²⁹ R. Nambu,²⁹ S. Nawang,¹² K. Nishikawa,¹¹ K. Nitta,¹⁶ F. Nova,¹ P. Novella,³² Y. Obayashi,²⁹ A. Okada,³⁰ K. Okumura,³⁰ S. M. Oser,³ Y. Oyama,¹¹ M. Y. Pac,⁷ F. Pierre,⁵ A. Rodriguez,¹ C. Saji,³⁰ M. Sakuda,²¹ F. Sanchez,¹ K. Scholberg,^8,18 R. Schroeter,⁹ M. Sekiguchi,¹⁴ M. Shiozawa,²⁹ K. Shiraishi,³³ G. Sitjes,³² M. Smy,⁴ H. Sobel,⁴ M. Sorel,³² J. Stone,² L. Sulak,² A. Suzuki,¹⁴ Y. Suzuki,²⁹ M. Tada,¹¹ T. Takahashi,¹² Y. Takenaga,³⁰ Y. Takeuchi,²⁹ K. Taki,²⁹ Y. Takubo,²² N. Tamura,²⁰ M. Tanaka,¹¹ R. Terri,²⁷ S. T'Jampens,⁵ A. Tornero-Lopez,³² Y. Totsuka,¹¹ M. Vagins,⁴ L. Whitehead,²⁷ C. W. Walter,⁸ W. Wang,² R. J. Wilkes,³³ S. Yamada,²⁹ Y. Yamada,¹¹ S. Yamamoto,¹⁶ C. Yanagisawa,²⁷ N. Yershov,¹³ H. Yokoyama,²⁸ M. Yokoyama,¹⁶ J. Yoo,²⁴ M. Yoshida,²² and J. Zalipska²⁵

(K2K Collaboration)

¹Institut de Fisica d'Altes Energies, Universitat Autonoma de Barcelona, E-08193 Bellaterra (Barcelona), Spain
²Department of Physics, Boston University, Boston, Massachusetts 02215, USA
³Department of Physics & Astronomy, University of British Columbia, Vancouver, British Columbia, Canada V6T 1Z1
⁴Department of Physics and Astronomy, University of California, Irvine, Irvine, California 92697-4575, USA
⁵DAPNIA, CEA Saclay, 91191 Gif-sur-Yvette Cedex, France
⁶Department of Physics, Chonnam National University, Kwangju 500-757, Korea
⁷Department of Physics, Dongshin University, Naju 520-714, Korea
⁸Department of Physics, Duke University, Durham, North Carolina 27708, USA
⁹DPNC, Section de Physique, University of Geneva, CH1211, Geneva 4, Switzerland
¹⁰Department of Physics and Astronomy, University of Hawaii, Honolulu, Hawaii 96822, USA
¹¹High Energy Accelerator Research Organization (KEK), Tsukuba, Ibaraki 305-0801, Japan
¹²Graduate School of Advanced Sciences of Matter, Hiroshima University, Higashi-Hiroshima, Hiroshima 739-8530, Japan
¹³Institute for Nuclear Research, Moscow 117312, Russia
¹⁴Kobe University, Kobe, Hyogo 657-8501, Japan
¹⁵Department of Physics, Korea University, Seoul 136-701, Korea
¹⁶Department of Physics, Kyoto University, Kyoto 606-8502, Japan
¹⁷Department of Physics and Astronomy, Louisiana State University, Baton Rouge, Louisiana 70803-4001, USA
¹⁸Department of Physics, Massachusetts Institute of Technology, Cambridge, Massachusetts 02139, USA
¹⁹Department of Physics, Miyagi University of Education, Sendai 980-0845, Japan
²⁰Department of Physics, Niigata University, Niigata, Niigata 950-2181, Japan
²¹Department of Physics, Okayama University, Okayama, Okayama 700-8530, Japan
²²Department of Physics, Osaka University, Toyonaka, Osaka 560-0043, Japan
²³University of Rome La Sapienza and INFN, I-000185 Rome, Italy
²⁴Department of Physics, Seoul National University, Seoul 151-747, Korea
²⁵A. Soltan Institute for Nuclear Studies, 00-681 Warsaw, Poland
²⁶Research Center for Neutrino Science, Tohoku University, Sendai, Miyagi 980-8578, Japan
²⁷Department of Physics and Astronomy, State University of New York, Stony Brook, New York 11794-3800, USA
²⁸Department of Physics, Tokyo University of Science, Noda, Chiba 278-0022, Japan
²⁹Kamioka Observatory, Institute for Cosmic Ray Research, University of Tokyo, Kamioka, Gifu 506-1205, Japan
³⁰Research Center for Cosmic Neutrinos, Institute for Cosmic Ray Research, University of Tokyo, Kashiwa, Chiba 277-8582, Japan
³¹TRIUMF, Vancouver, British Columbia, Canada V6T 2A3
³²Instituto de Física Corpuscular, E-46071 Valencia, Spain
³³Department of Physics, University of Washington, Seattle, Washington 98195-1560, USA
³⁴Institute of Experimental Physics, Warsaw University, 00-681 Warsaw, Poland

The atmospheric neutrino background for proton decay via p-->e⁺pi⁰ in ring imaging water Cherenkov detectors is studied with an artificial accelerator neutrino beam for the first time. In total, 3.14×10⁵ neutrino events corresponding to about 10 megaton-years of atmospheric neutrino interactions were collected by a 1000 ton water Cherenkov detector (KT). The KT charged-current single pi⁰ production data are well reproduced by simulation programs of neutrino and secondary hadronic interactions used in the Super-Kamiokande (SK) proton decay search. The obtained p-->e⁺pi⁰ background rate by the KT data for SK from the atmospheric neutrinos whose energies are below 3 GeV is 1.63_-0.33^+0.42(stat)_-0.51^+0.45(syst)(megaton-year)^-1. This result is also relevant to possible future, megaton-scale water Cherenkov detectors.

©2008 The American Physical Society

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