Search for Heavy Neutrinos in Kaon Decay

Abstract

We obtained a new constraint of | u . 1 * * versus m(v.), as shown in Fig.l. Because or the better resolution the lower end of the neutrino mass was reduced to 40 MeV. In Fig.l are also shown other upper limits. One is from R -» j/v done /3/ at SIN. Another comes from the 1 He(jf ,v ) reaction /4/. 1 For the first time we obtained e + spectrum with rejection of the three body decay mode. Hitherto only the e v peak region of 247 MeV/c was known /$/. From the analysis oj; the spectrum we obtained a new constraint, on I U | in a wide mass range between 140 and 350 MeV, as shown in Fig.2. The JL* -> e y experiment /6/ at TRIUMF covers a complementary mass region. A recent experiment to search for neutrino0decays at CERN /?/ gave a new constraint on |U | but the present experiment has yielded a one-order of magnitude better constraint. It should be noted that the deduction of | l I e i l from the CERN experiment requires a model for heavy neutrino decay, while in the present experiment it is given purely kmematically,