Neutrino mixing and oscillations

摘要

In quantum mechanics, an eigenstate of an observable that does not commute with the Hamiltonian can evolve out of that state through time evolution, with the result that a measurement may result in an eigenvalue other than of the initial eigenstate. This property of "mixing" manifests itself in neutrinos in a particularly profound and dramatic way through the phenomenon of neutrino oscillations[1,2]. In particular, neutrinos can be identified in two ways: how they interact via the weak interaction and what their masses are, corresponding to flavor and mass (energy) eigenstates respectively. The former is the basis for determining the weak interaction properties of the neutrino (which charged lepton results when it is produced by decay or interacts), whereas the latter governs how the neutrino evolves in time. General considerations of quantum mechanics dictate that the two bases should be related by a unitary transformation: |v_a〉 = Σ_iU_(αi)~*|v_i〉, where α and i label the flavor and mass eigenstates, respectively.