Hierarchy independent sensitivity to leptonic δCP with atmospheric neutrinos

The Dirac leptonic CP phase δCP is one of the crucial unknown parameters in neutrino oscillation physics. In this paper we explore the possibility of using low energy atmospheric neutrino events to probe δCP. We show that at sub-GeV energies, when the events are binned as a function of the energy and direction of the final state leptons, a consistent distinction between various input δCP values is obtained. More importantly, we show that at these energies there is no sensitivity to the neutrino mass ordering/hierarchy, so that δCP can be measured without hierarchy ambiguity. A χ2 analysis of the sensitivity to δCP using atmospheric neutrinos assuming an isoscalar detector that cannot separate νe and ν¯e events is done. While exceedingly high sensitivities are obtained in the ideal case, a modest sensitivity remains when the effects of energy resolution and systematic uncertainties are taken into account.