Chapter 1 - Neutrino Properties and Its Interactions

Summary

Historical Introduction to Neutrinos

Neutrino hypothesis

Beginning with the neutrino hypothesis proposed by Pauli in 1930, the storyof the neutrino has been an amazing one [1]. It all started with a letterwritten by Pauli to the participants of a nuclear physics conference inTubingen, Germany, on December 4, 1930 [1], in which he proposed theexistence of a new neutral weakly interacting particle of spin and called it“neutron” as a “verzweifelten Ausweg” (desperateremedy), to explain the two outstanding problems in contemporary nuclearphysics which posed major difficulties with respect to thescientists’ theoretical interpretations. These two problems wererelated with the puzzle of energy conservation inβ-decays of nuclei [2, 3], discovered by Chadwick in1914 [4], and anomalies in understanding the spin–statistics relationin the case of ¹⁴N and ⁶Li nuclei within the contextof the nuclear structure model that was prevalent in the early decades ofthe twentieth century [5, 6] in which electrons and protons were consideredto be nuclear constituents.

This proposed ‘verzweifelten Ausweg’ was considered sotentative by Pauli himself that he postponed its scientific publication byalmost three years. Today, neutrinos, starting from being a mere theoreticalidea of an undetectable particle, are known to be the most abundantparticles in the universe after photons, being present almost everywherewith a number density of approximately 330/cm³ pan universe. Thehistory of the progress of our understanding of the physics of neutrinos isfull of surprises; neutrinos continue to challenge our expectationsregarding the validity of certain symmetry principles and conservation lawsin particle physics. The study of neutrinos and their interaction withmatter has made many important contributions to our present knowledge ofphysics, which are highlighted by the fact that ten Nobel Prizes have beenawarded for physics discoveries in topics either directly in the field ofneutrino physics or in the topics in which the role of neutrino physics hasbeen very crucial.

In this chapter, we will provide a historical introduction to the developmentof our understanding of neutrinos and their properties as they have emergedfrom the theoretical and experimental studies made over the last 90years.