Feature Article: Neutrino Physics

Abstract

It was a desperate attempt to rescue energy and angular momentum conservation in beta decays when Wolfgang Pauli postulated the neutrino in 1930. In his famous letter addressed to a meeting in Tübingen, Germany, Pauli expressed his apprehension that this new neutral and almost massless particle may never get detected experimentally. Indeed it took 26 years until F. Reines (Nobel prize 1995) and C. Cowan observed neutrinos via the inverse beta decay reaction which are emitted from the fission products in a nuclear power reactor. Neutrinos only interact with matter via weak forces and the cross section was measured to be σ = (1.1 ± 0.3) 10−43 cm2, which corresponds to an enormous absorption length of about 29 light years! In 1957 parity violation in weak interaction was detected by C. Wu and only one year later the helicity of neutrinos by a famous experiment performed by M. Goldhaber. He found the neutrino to be left handed, whereas the anti-neutrino is right handed. Since the right handed partner of the neutrino is missing, neutrinos are massless in the standard model. If the anti-neutrino is identical to the neutrino it is called Majorana particle.