Correlations of errors in a CP-violation neutrino factory experiment

An indirect CP-violation neutrino factory experiment is studied, including simul taneous correlations of errors of the six oscillation parameters and a matter ef fect normalisation parameter, C. It is found that for larger values of $\theta_{13}$ ($3^\circ$), an uncertainty on the matter effect of the order 5% means t hat the optimal baseline for measurement of $\delta$ is reduced from 3000km to 2 000km. When the background fraction is assumed to be $10^{-3}$ the optimal muon energy is also reduced from 50GeV to around 20GeV. An experiment with L=2000km, $E_\mu=$20GeV is found to be sensitive to non-zero $\delta$ down to around $\t heta_{13}\approx0.3^\circ$.