An illustration and analysis of the degeneracy in the search for the leptonic CP-violating phase and the neutrino mass hierarchy

[出版社版]Determination of the value of the leptonic CP-violating phase delta and the neutrino mass hierarchy sgn delta m(31)(2) through long baseline neutrino oscillation experiments is systematically analyzed. We note that the two oscillation spectra are difficult to discriminate and lead to the degeneracy when they are peaked at the same energy and have the same peak probability. The condition of peak-matching is therefore introduced as a criterion for the presence of degeneracy. The matching of peaks is visualized as an intersection of trajectories traced by the peak of an oscillation spectrum while the value of delta is varied from 0 to 2 pi. We numerically calculate a pair of trajectories for a pair of hierarchies and examine the degeneracy, especially that concerning the hierarchy. We formulate the trajectory in terms of analytic expressions and evaluate the critical length, which is shown to be proportional, to 1/ sin theta(13). In view of our analysis, we discuss future prospects to solve the hierarchy degeneracy with regard to the following four approaches: elongating the baseline length sufficiently, using both neutrinos and anti-neutrinos, combining experiments with different baseline lengths, and observing two or more oscillation peaks