The NA62 experiment recorded a large sample of K+ -> mu(+)nu(mu)decays in 2007. A peak search has been performed in the reconstructed missing mass spectrum. In the absence of a signal, limits in the range 2 x10(-6) to 10(-5) have been set on the squared mixing matrix element |U-mu 4|(2) between muon and heavy neutrino states, for heavy neutrino masses in the range 300-375MeV/c(2). The result extends the range of masses for which upper limits have been set on the value of |U mu(4)|(2) in previous production search experiments. (C) 2017 The Author(s). Published by Elsevier B.V.
