Leptonic CP violation search and the ambiguity of delta m(31)(2)

Abstract

We consider a search for the CP-violating angle δCP in long baseline neutrino oscillation experiments. We show that the subleading δCP-dependent terms in the νµ → νe oscillation probability can be easily obscured by the ambiguity of the leading term which depends on |δm 2 31|. It is thus necessary to determine the value of δm312 with a sufficient accuracy. The νµ survival events, which can be accumulated simultaneously with the νe appearance events, can serve for this purpose owing to its large statistics. Therefore, the combined analysis of νe appearance and νµ survival events is crucial to provide a restrictive constraint on δCP. Taking a test experimental setup, we demonstrate in the δCP -δm312 plane that the analysis of νe appearance events leads to less restrictive constraints on the value of δCP due to the ambiguity of δm312 and that the combined analysis efficiently improves the constraints.