Historical Introduction to Neutrinos
Beginning with the neutrino hypothesis proposed by Pauli in 1930, the story of the neutrino has been an amazing one . It all started with a letter written by Pauli to the participants of a nuclear physics conference in Tubingen, Germany, on December 4, 1930 , in which he proposed the existence of a new neutral weakly interacting particle of spin and called it “neutron” as a “verzweifelten Ausweg” (desperate remedy), to explain the two outstanding problems in contemporary nuclear physics which posed major difficulties with respect to the scientists’ theoretical interpretations. These two problems were related with the puzzle of energy conservation in β-decays of nuclei [2, 3], discovered by Chadwick in 1914 , and anomalies in understanding the spin–statistics relation in the case of 14N and 6Li nuclei within the context of the nuclear structure model that was prevalent in the early decades of the twentieth century [5, 6] in which electrons and protons were considered to be nuclear constituents.
This proposed ‘verzweifelten Ausweg’ was considered so tentative by Pauli himself that he postponed its scientific publication by almost three years. Today, neutrinos, starting from being a mere theoretical idea of an undetectable particle, are known to be the most abundant particles in the universe after photons, being present almost everywhere with a number density of approximately 330/cm3 pan universe. The history of the progress of our understanding of the physics of neutrinos is full of surprises; neutrinos continue to challenge our expectations regarding the validity of certain symmetry principles and conservation laws in particle physics. The study of neutrinos and their interaction with matter has made many important contributions to our present knowledge of physics, which are highlighted by the fact that ten Nobel Prizes have been awarded for physics discoveries in topics either directly in the field of neutrino physics or in the topics in which the role of neutrino physics has been very crucial.
In this chapter, we will provide a historical introduction to the development of our understanding of neutrinos and their properties as they have emerged from the theoretical and experimental studies made over the last 90 years.