Large matter effects in νμ→ντ oscillations -: art. no. 051801

We show that matter effects change the nu(mu) --> nu(tau) oscillation probability by as much as 70% for certain ranges of energies and path lengths. Consequently, the nu(mu) --> nu(mu) survival probability also undergoes large changes. A proper understanding of nu(mu) survival rates must consider matter effects in P-mutau as well as P-mue. We comment on (a) how these matter effects may be observed and the sign of Delta(31) determined in atmospheric neutrino measurements and at neutrino factories, and (b) how they lead to heightened sensitivity for small theta(13).