This chapter focusses on the properties of neutrinos and in particular the phenomenon of neutrino oscillations, whereby neutrinos undergo flavour transitions as they propagate over large distances. Neutrino oscillations are a quantum-mechanical phenomenon and can be described in terms of the relationship between the eigenstates of the weak interaction νe, νμ and ντ, and the eigenstates of the free-particle Hamiltonian, known as the mass eigenstates, ν1, ν2 and ν3. The mathematical description of neutrino oscillations is first introduced for two flavours and then extended to three flavours. The predictions are compared to the recent experimental data from reactor and long-baseline neutrino oscillation experiments.
Neutrino flavours
Unlike the charged leptons, which can be detected from the continuous track defined by the ionisation of atoms as they traverse matter, neutrinos are never directly observed; they are only detected through their weak interactions. Different neutrino flavours can only be distinguished by the flavours of charged lepton produced in charged-current weak interactions. Consequently, the electron neutrino νe, is defined as the neutrino state produced in a charged-current weak interaction along with an electron. Similarly, by definition, the weak charged-current interactions of a νe will produce an electron. For many years it was assumed that the νe, νμ and ντ were massless fundamental particles. This assumption was based, at least in part, on experimental evidence. For example, it was observed that the interactions of the neutrino/antineutrino produced along with a positron/electron in a nuclear β-decay, would produce an electron/positron as indicated in Figure 13.1.
Review the options below to login to check your access.
Log in with your Cambridge Aspire website account to check access.
If you believe you should have access to this content, please contact your institutional librarian or consult our FAQ page for further information about accessing our content.