Physics Letters B 278 (1992) 217-220 P HYSIC S LETTERS B North-Holland A limit on spontaneous R parity breaking from Kamiokande M. Mori, M.M. Nojiri 1,2, y. Oyama, A. Suzuki, K. Takahashi, M. Yamada National Laboratory for High Energy Physics (KEK), Tsukuba, Ibaraki 305, Japan H. Takei, K. Miyano, H. Miyata Niigata University, Niigata 950-21, Japan K.S. Hirata, K. Inoue, T. Ishida, T. Kajita, K. Kihara, M. Nakahata, K. Nakamura, N. Sato 3 Y. Suzuki, Y. Totsuka, Y. Yaginuma 4 Institute for Cosmic Ray Research, University of Tokyo, Tanashi, Tokyo 188, Japan M. Koshiba, K. Nishijima Tokai University, Shibuya, Tokyo 151, Japan T. Kajimura, T. Suda, T. Tajima 5 Department of Physics, Kobe University, Kobe, Hyogo 657, Japan Y. Fukuda, E. Kodera, Y. Nagashima, M. Takita Department of Physics, Osaka University, Toyonaka, Osaka 560, Japan K. Kaneyuki and T. Tanimori Department of Physics, Tokyo Institute of Technology, Meguro, Tokyo 152, Japan Received 9 December 1991 If R parity is not an exact symmetry in supersymmetric theories, the lightest supersymmetric partner, most favorably the neu- tralino, would not be stable, but may decay to produce energetic neutrinos. We show that a lack of excess neutrino events above the atmospheric neutrino background, obtained from upward-going muon data in Kamiokande, places a severe constraint on models of R parity breaking if the neutralino is a dark-matter particle. The stability of the lightest supersymmetric part- ner (LSP) is derived on the ad hoc postulation in su- JSPS Fellowship for Japanese Junior Scientists. 2 Work partially supported by the Grant-in-Aid for Scientific Research from the Ministry of Education, Science and Cul- ture ( # 02952050). 3 Present address: National Laboratory for High Energy Phys- ics (KEK), Tsukuba, Ibaraki 305, Japan. 4 Present address: Institute of Industrial Science, University of Tokyo, Roppongi, Tokyo 106, Japan. 5 Present address: Maruzen Co., Ltd., Nihonbashi, Tokyo 103, Japan. persymmetric theories of exact R parity conserva- tion. If R parity is violated in some way, one may expect many observable phenomena, some of which are already constrained by experiments [ 1 ] and as- trophysical observations [ 2 ]. In particular, a model of very small R parity breaking via spontaneous sym- metry breaking has been proposed, which retains most of the usual supersymmetric predictions at the labo- ratory, but has testable astrophysical and cosmologi- cal consequences [ 3,4 ]. In the model of Berezinsky, Masiero and Valle [ 4 ], additional isosinglet superfields (v c, S~) are intro- 0370-2693/92/$ 05.00 © 1992 Elsevier Science Publishers B.V. All rights reserved. 217