Search For Heavy Neutrinos In K+ -> Mu(+)Nu(H) Decays

Evidence of a heavy neutrino, nu(H), in the K+ -> mu(+)nu(H) decays was sought using the E949 experimental data with an exposure of 1.70 x 10(12) stopped kaons. With the major background from the radiative K+ -> mu(+)nu(mu)gamma decay understood and suppressed, upper limits (90% C.L.) on the neutrino mixing matrix element between the muon and heavy neutrinos, vertical bar U-mu H vertical bar(2), were set at the level of 10(-7) to 10(-9) for the heavy neutrino mass region 175 to 300 MeV/c(2).