The LMA MSW Solution of the Solar Neutrino Problem, Inverted Neutrino Mass Hierarchy and Reactor Neutrino Experiments

Original · EN

In the context of three-neutrino oscillations, we study the possibility of using antineutrinos from nuclear reactors to explore the 10⁻⁴ eV² < 8× 10⁻⁴ eV² region of the LMA MSW solution of the solar neutrino problem and measure with high precision. The KamLAND experiment is not expected to determine if the latter happens to lie in the indicated region. By analysing both the total event rate suppression and the energy spectrum distortion caused by νₑ oscillations in vacuum, we show that the optimal baseline of such an experiment is L (20 - 25) km. Furthermore, for 10⁻⁴ eV² < 5× 10⁻⁴ eV², the same experiment might be used to try to distinguish between the two possible types of neutrino mass spectrum - with normal or with inverted hierarchy, by exploring the effect of interference between the atmospheric- and solar- Δm² driven oscillations; for larger values of not exceeding 8.0× 10⁻⁴ eV², a shorter baseline, L 10 km, would be needed for the purpose. The indicated interference effect modifies in a characteristic way the energy spectrum of detected events. Distinguishing between the two types of neutrino mass spectrum requires, however, a high precision determination of the atmospheric Δm², a sufficiently large ²θand a non-maximal ²2θ, where θand θ are the mixing angles respectively limited by the CHOOZ and Palo Verde data and characterizing the solar neutrino oscillations. It also requires a relatively high precision measurement of the positron spectrum in the reaction νₑ + p → e⁺ + n.