Matter versus vacuum oscillations at long-baseline accelerator neutrino experiments

The neutrino oscillation probabilities at the long-baseline accelerator experiments are expected to be modified by matter effects. We search for evidence of such modification in data T2K and NO$\nu$A, fitting hypothesis (a) oscillations (b) vacuum oscillations. find that provide as good a fit Even extended runs with 5 years mode $(5 \nu)$ five anti-neutrino \bar{\nu})$, can {\bf not} make $3~\sigma$ distinction between proposed experiment DUNE, each \nu + rule out itself $5~\sigma$ if hierarchy is normal. If inverted, discrimination against requires combination \bar{\nu})$ T2K, \nova DUNE.