Leptonic CP Violation Search and the Ambiguity of dm²₃1

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We consider a search for the CP-violating angle deltaCP in long baseline neutrino oscillation experiments. We show that the subleading deltaCP-dependent terms in the nuₘu -> nuₑ oscillation probability can be easily obscured by the ambiguity of the leading term which depends on |dm²₃1|. It is thus necessary to determine the value of dm²₃1 with a sufficient accuracy. The nuₘu survival events, which can be accumulated simultaneously with the nuₑ appearance events, can serve for this purpose owing to its large statistics. Therefore, the combined analysis of nuₑ appearance and nuₘu survival events is crucial to provide a restrictive constraint on deltaCP. Taking a test experimental setup, we demonstrate in the deltaCP-dm²₃1 plane that the analysis of nuₑ appearance events leads to less restrictive constraints on the value of deltaCP due to the ambiguity of dm²₃1 and that the combined analysis efficiently improves the constraints.