We propose a way of detecting $\mathit{CP}$ violation in a single neutrino oscillation channel at very long baselines (on the order of several thousands of kilometers), given precise knowledge of the smallest mass-squared difference. It is shown that $\mathit{CP}$ violation can be characterized by a shift in $L/E$ of the peak oscillation in the ${\nu }_e\text{−}{\nu }_{\mu }$ appearance channel, both in vacuum and in matter. In fact, matter effects enhance the shift at a fixed energy. We consider the case in which sub-GeV neutrinos are measured with varying baseline and also the case of a fixed baseline. For the varied baseline, accurate knowledge of the absolute neutrino flux would not be necessary; however, neutrinos must be distinguishable from antineutrinos. For the fixed baseline, it is shown that $\mathit{CP}$ violation can be distinguished if the mixing angle ${\theta }_{13}$ were known.

• Received 12 September 2007

DOI:https://doi.org/10.1103/PhysRevC.76.055502