IsCPviolation observable in long baseline neutrino oscillation experiments?

We have studied $\mathrm{CP}$ violation originating from the phase of the neutrino-mixing matrix in the long baseline neutrino oscillation experiments. The direct measurement of $\mathrm{CP}$ violation is the difference of the transition probabilities between $\mathrm{CP}$-conjugate channels. In those experiments, the $\mathrm{CP}$-violating effect is not suppressed if the highest neutrino mass scale is taken to be 1–5 eV, which is appropriate for the cosmological hot dark matter. Assuming the hierarchy for the neutrino masses, the upper bounds of $\mathrm{CP}$ violation have been calculated for three cases, in which mixings are constrained by the recent short baseline ones. The calculated upper bounds are larger than ${10}^{-2}$, which will be observable in the long baseline accelerator experiments. The matter effect, which is not CP invariant, has been also estimated in those experiments.