Hierarchy independent sensitivity to leptonic δ<inf>CP</inf> with low energy atmospheric neutrinos

One of the important unknowns in neutrino oscillation physics is the leptonic CP phase δCP. Because of the ambiguity between δCP and neutrino mass hierarchy, experiments have to be designed in such a way as to measure these parameters independent of each other. Long baseline experiments like DUNE is exclusively designed to measure δCP in regions without hierarchy ambiguity and atmospheric neutrino experiments like INO are designed to measure hierarchy without δCP ambiguity. However atmospheric neutrinos are not usually used to probe δCP. Here we present that, sub-GeV energy atmospheric neutrinos can be used to probe δCP irrespective of mass hierarchy. We show that when the events are binned as a function of (Elobs,cosθlobs), the observed energy and direction of the final state leptons in charged current interactions of ν and ν, a consistent distinction between various δCP values is obtained. Since there is no sensitivity to the mass ordering/hierarchy, δCP can be measured without hierarchy ambiguity at these energies. Sensitivity studies with ideal as well as realistic cases are discussed.