Ambiguities of theoretical parameters and CP/T violation in neutrino factories

We study the optimal setup for observation of the CP asymmetry in neutrino factory experiments --- the baseline length, the muon energy and the analysis method. First, we point out that the statistical quantity which has been used in previous works doesn't represent the CP asymmetry, and hence cannot be used to measure it. Then we propose the more suitable quantity, $\equiv \chi^{2}_{2}$, which is sensitive to the CP asymmetry. We investigate the behavior of $ \chi^{2}_{2}$ with ambiguities of the theoretical parameters. The fake CP asymmetry due to the matter effect increases with the baseline length. Therefore, the error in the estimation of the fake CP asymmetry grows with the baseline length due to the ambiguities of the theoretical parameters. Thus we insist that we lose the sensitivity to the genuine CP-violation effect in longer baseline such as $ L \geq 1000$ km Finally we examine the T-violation mode. We show that in this mode the genuine CP asymmetry is observed very clearly even if we have the ambiguities in the theoretical parameters.