Limits on the existence of heavy neutrinos in the range 50-1000 eV from the study of the 187Re beta decay.
We analyzed the spectrum of the 187Re beta decay, obtained with a cryogenic microcalorimeter, searching for heavy neutrinos in the mass range 50-1000 eV. No evidence has been found for them and the upper limits on the mixing angle with a zero-mass neutrino are reported. Upper limits of 9x10(-3) at 1000 eV/c(2), 1.2x10(-2) at 500 eV/c(2), 4.4x10(-2) at 200 eV/c(2), and 0.116 at 100 eV/c(2) at 95% C.L. have been obtained. These upper limits are a factor of 2 to 4 lower than the current limits reported in the literature.
Galeazzi
M
M
INFN of Genoa and Genoa University, Via Dodecaneso 33, I-16146 Genoa, Italy.
Fontanelli
F
F
Gatti
F
F
Vitale
S
S