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Search for the decay K→πν in the momentum region P<195 MeV/c

2002; Elsevier BV; Volume: 537; Issue: 3-4 Linguagem: Inglês

10.1016/s0370-2693(02)01911-1

1873-2445

S. S. Adler, M. Aoki, M. Ardebili, M. S. Atiya, A. O. Bazarko, P. C. Bergbusch, B. Bhuyan, E. W. Blackmore, D. Bryman, I-H. Chiang, M. R. Convery, M. Diwan, James S. Frank, J. S. Haggerty, T. Inagaki, M. Ito, V. Jain, D. E. Jaffe, S. Kabe, M. Kazumori, S. H. Kettell, P. Kitching, M. Kobayashi, T. K. Komatsubara, A. Konaka, Y. Kuno, M. Kuriki, T. F. Kycia, K. K. Li, L. Littenberg, D. Marlow, R. A. McPherson, J. A. Macdonald, P. D. Meyers, J. Mildenberger, N. Muramatsu, T. Nakano, C. Ng, Sam Yanwing Ng, T. Numao, J.-M. Poutissou, R. Poutissou, G. Redlinger, T. Sasaki, Takahiro Sato, T. Shinkawa, F. C. Shoemaker, A. Smith, R. Soluk, J. R. Stone, R. C. Strand, S. Sugimoto, Y. Yoshimura, C. Witzig,

High-Energy Particle Collisions Research

We have searched for the decay $K^+ \to \pi^+ \nu \bar\nu$ in the kinematic region with pion momentum below the $K^+ \to \pi^+ \pi^0$ peak. One event was observed, consistent with the background estimate of $0.73\pm 0.18$. This implies an upper limit on $B(K^+ \to \pi^+ \nu \bar\nu)< 4.2\times 10^{-9}$ (90% C.L.), consistent with the recently measured branching ratio of $(1.57^{+1.75}_{-0.82}) \times 10^{-10}$, obtained using the standard model spectrum and the kinematic region above the $K^+ \to \pi^+ \pi^0$ peak. The same data were used to search for $K^+ \to \pi^+ X^0$, where $X^0$ is a weakly interacting neutral particle or system of particles with $150 < M_{X^0} < 250 {\rm ~MeV/c^2}$.