2026-07-072026-07-07http://salesiana.dossiersoluciones.com/handle/123456789/188191We show that the earth matter effects in the ${\rm {ν_e \to ν_e}}$ survival probability can be used to cleanly determine the third leptonic mixing angle $θ_{13}$ and the sign of the atmospheric neutrino mass squared difference, $Δm^2_{31}$, using a $β$-beam as a $ν_e$ source.4 pages, 4 eps figures; comments and references added, to appear in Phys. Rev. DHigh Energy Physics - PhenomenologyHigh Energy Physics - Experimenttext