Effects of Matter in Neutrino Oscillations and Determination of Neutrino   Mass Hierarchy at Long-baseline Experiments
  Neutrino oscillations change when in media in comparison to vacuum oscillations due to the scattering of neutrinos on matter constituents, electrons particularly. This can be easily described by introducing new effective matter mixing angles and squared mass-splittings. Exploiting the matter effects and subsequent enhancement or suppression of oscillation probabilities can be used to determine the hierarchy of neutrino mass states. Recent long-baseline experiments NO$\nu$A and T2K investigate this possibility. Together NO$\nu$A and T2K combined can reject the wrong hierarchy for more than 20% of all possible values of yet unknown CP violating phase $\delta$ $\in$ [-180$^\circ$, 180$^\circ$]. 
Tomas Nosek
hep-ph