Search for Heavy Neutrino in K->mu nu_h(nu_h-> nu gamma) Decay at ISTRA+   Setup
  Heavy neutrino nu_h with m_h < 300MeV/c^2 can be effectively searched for in kaon decays. We put upper limits on mixing matrix element |U_mu_h}|^2 for radiatively decaying nu_h from K->mu nu_h (nu_h -> nu gamma) decay chain in the following parameter region: 30MeV/c^2 < m_h < 80MeV/c^2; 10^{-11}sec < tau_h < 10^{-9}sec. For the whole region |U_{mu h}|^2 < 5 x 10^{-5} for Majorana type of nu_h and | U_{\mu h}|^2 < 8 x 10^{-5} for the Dirac case. 
ISTRA+ collaboration: V. A. Duk, V. N. Bolotov, A. A. Khudyakov, V. A.   Lebedev, A. I. Makarov, V. P. Novikov, A. Yu. Polya...
hep-ex