Determination of the neutrino mass hierarchy in the regime of small matter effect

We point out a synergy between T-conjugated oscillation channels in the determination of the neutrino mass hierarchy with oscillation experiments with relatively short baselines (L < 700 km), where the matter effect is small. If information from all four oscillation channels $\nu_\mu\to\nu_e$, $\bar\nu_\mu\to\bar\nu_e$, $\nu_e\to\nu_\mu$ and $\bar\nu_e\to\bar\nu_\mu$ is available, a matter effect of few percent suffices to break the sign-degeneracy and allows to determine the neutrino mass hierarchy. The effect is discussed by analytical considerations of the relevant oscillation probabilities, and illustrated with numerical simulations of realistic experimental setups. Possible configurations where this method could be applied are the combination of a super beam experiment with a beta beam or a neutrino factory, or a (low energy) neutrino factory using a detector with muon and electron charge identification.