A lot of progress has been made in our understanding of the neutrinos over the last 30 years, since the discovery of neutrino oscillation by the SuperKamiokande experiment. Among the pending questions, we can list:
- Is there a 4th neutrino (which would be sterile) ? There is an important experimental effort.
- The mass determination. We know two Δm2, but not the absolute value of the mass, having however an upper limit (~1 eV) on the total sum of the masses of the three neutrinos.
- The mass hierarchy (neutrino mass ordering).
- The CP violation δCP in the neutrino sector.
- Is the neutrino its own antiparticle (i.e. Majorana or Dirac neutrino)? The answer will come from the 0νββ double beta decay experiments.
- The detection of cosmological neutrinos