Search for heavy neutrinos in $K^{+}\to \hat{I}{¼}^{+}\hat{I}{½}_H$ decays

Abstract

Evidence of a heavy neutrino, $\hat{I}{½}_H$, in the $K^{+}\to \hat{I}{¼}^{+}\hat{I}{½}_H$ decays was sought using the E949 experimental data with an exposure of $1.70\times 10^{12}$ stopped kaons. With the major background from the radiative $K^{+}\to \hat{I}{¼}^{+}\hat{I}{½}_{\hat{I}}¼{\hat{I}}^3$ decay understood and suppressed, upper limits (90% C.L.) on the neutrino mixing matrix element between muon and heavy neutrino, $|U_{\hat{I}¼H}{|}^2$, were set at the level of $10^{-7}$ to $10^{-9}$ for the heavy neutrino mass region 175 to 300 MeV/$c^2$.

14 pages, 13 figures; accepted by Physical Review D