  Determination of the value of the leptonic CP-violating phase deltaand the
neutrino mass hierarchy sgn(dm2_31) through long baselineneutrino oscillation
experiments is systematically analyzed. We notethat the two oscillation spectra
are difficult to discriminate andlead to the degeneracy when they are peaked at
the same energy andhave the same peak probability. The condition of
peak-matching istherefore introduced as a criterion for the presence of
degeneracy.The matching of peaks is visualized as an intersection of
trajectoriestraced by the peak of an oscillation spectrum while the value of
deltais varied from 0 to 2pi. We numerically calculate a pair oftrajectories
for a pair of hierarchies and examine the degeneracy,especially that concerning
the hierarchy. We formulate the trajectoryin terms of analytic expressions and
evaluate the critical length,which is shown to be proportional to
1/sin(theta_13). In view of ouranalysis, we discuss future prospects to solve
the hierarchydegeneracy with regard to the following four approaches:
elongatingthe baseline length sufficiently, using both neutrinos
andanti-neutrinos, combining experiments with different baseline lengths,and
observing two or more oscillation peaks.
