Neutrinos as a portal to physics beyond the Standard Model:

Neutrinos are among the most elusive elementary particles in our universe known to date. Their existence was initially postulated by W. Pauli and E. Fermi in the 1930's to explain radioactive beta decay and experimentally confirmed by C. Cowan and F. Reines in 1956. They are electrically neutral and interact with matter exclusively via the Weak nuclear force, thus making their detection quite challenging. Formally they play an essential role in the electroweak theory of elementary particles, which by construction accommodates only massless neutrinos, even in the presence of the recently discovered scalar Higgs field. The Standard Model theory implies the existence of minimally three species of massless neutrinos: the electron, muon and tau neutrino.