Ask A Scientist© Astronomy Archive

Author:      john wofford
Does a neutrino have a measurable mass?

Response #:  1 of 1 
Author:      jasjeet s bagla
Experiments have not been able to detect any sign of neutrino's mass.  This
only puts an upper limit on the mass, this limit however is very close to
zero for the electron neutrino.  There are two other kinds of neutrinos - mu
and tau.  The upper limit on masses for these is fairly high.  Theory does
not predict anything very strongly, though the standard model of particle
physics sets the masses of all three neutrinos to zero.  There are some
problems like the solar neutrino problem and the atmospheric neutrino
problem, whose solution requires at least two neutrino species to be
massive.  It also requires something called mixing of neutrino types
(flavors).  A massive neutrino might aid formation of galaxies.  Lastly,
there is a very strong upper limit on neutrino masses coming from cosmology. 
This means that you cannot have massive neutrinos with an arbitrary mass.