Observation of neutrinos emitted by the supernova SN1987a in the large Magellanic Cloud place an upper limit on the rest mass energy of the electron neutrino of 20 eV. If the rest energy of the neutrino, rather than being zero, is in fact equal to 20 eV, we have to find how much slower than light is a 1.5-MeV neutrino, emitted in a -decay.

Solution:             Click For PDF Version

We assume that the rest mass energy of the electron neutrino

The relativistic energy of a particle of rest mass energy moving with speed is given by the expression

A 1.5 MeV neutrino will therefore be moving with speed v ,which is related to the energy E and the rest mass energy by the following relation: