Hierarchy Sensitivity with Combined Standard and Rock Muons in ICAL at India-Based Neutrino Observatory

The neutrino mass ordering of the third mass eigen state vis-a-vis the first remains one of the undetermined parameters of neutrino physics. The proposed magnetized iron calorimeter detector (ICAL) at the India-based Neutrino Observatory (INO) has good sensitivity to this mass ordering, which it achieves by its capacity to distinguish neutrino and anti-neutrino-induced events through its charge identification capability. The charged current (CC) interactions of atmospheric muon neutrinos with the ICAL detector will produce muons and hadrons. The atmospheric muon neutrinos can also interact with the rock material surrounding the detector and produce muons and hadrons in corresponding CC interactions with the rock. While the hadrons get absorbed in the rock, some of these muons will reach the detector and get detected as well. We show that the combined sensitivity exceeds the sum of the two sensitivities by comparing the $$\Delta {\chi ^2}$$ for the two cases. We discuss their significance for INO.