Neutrino Oscillation Experiments at Nuclear Power Reactors

Abstract

The question whether the neutrino possesses a finite rest mass remains one of the most important and challenging issues in todays physics. Unfortunately, there is little guidance from theory. Whereas in the minimal version of Grand Unified Theories — the SU(5) model — there is no room for neutrino mass generating processes, extended models beyond SU(5) easily allow neutrino masses in the range 10^-6 eV to 10 eV. A finite neutrino mass together with violation of lepton number conservation offers the possibility of neutrino oscillations [1]. The underlying assumption for the existence of v — oscillations is, that the neutrino v _ℓ being created and detected by weak interaction processes are coherent superpositions of neutrino states v _i with definite mass m_i, in analogy to the KM — mixing of hadronic charged currents:

$$ {v_{\ell }} = \sum {{U_{{\ell, {i^v}i}}}\ell = e,\mu, \tau \ldots i = 1,2,3 \ldots } $$

(1)

where U _ℓ,i are the mixing amplitudes. In the simplest picture, where only two neutrino species are involved, neutrino oscillations are characterized by two parameters: the mixing angle Θ, denoting the degree of admixture of the neutrino mass eigenstates to the weak eigenstates and the mass parameter Δm² = |m₁ ² – m₂ ²| defined by the difference of the squared corresponding mass eigenvalues.