Super-PINGU for measurement of the leptonic CP-phase with atmospheric neutrinos

Abstract

We explore a possibility to measure the CP-violating phase $\delta$ using multi-megaton scale ice or water Cherenkov detectors with low, $(0.2 - 1)$ GeV, energy threshold assuming that the neutrino mass hierarchy is identified. We elaborate the relevant theoretical and phenomenological aspects of this possibility. The distributions of the $\nu_\mu$ (track) and $\nu_e$ (cascade) events in the neutrino energy and zenith angle $(E_\nu - \theta_z)$ plane have been computed for different values of $\delta$. We study properties and distinguishability of the distributions before and after smearing over the neutrino energy and zenith angle. The CP-violation effects are not washed out by smearing, and furthermore, the sensitivity to $\delta$ increases with decrease of the energy threshold. The $\nu_e$ events contribute to the CP-sensitivity as much as the $\nu_\mu$ events. While sensitivity of PINGU to $\delta$ is low, we find that future possible upgrade, Super-PINGU, with few megaton effective volume at ($0.5 - 1$) GeV and e.g. after 4 years of exposure will be able to disentangle values of $\delta = \pi/2,~ \pi,~ 3\pi/2$ from $\delta = 0$ with "distinguishability" ($\sim$ significance in $\sigma$'s) $S_{\sigma}^{tot} = (3 - 8),~ (6 - 14),~(3 - 8)$ correspondingly. Here the intervals of $S_{\sigma}^{tot}$ are due to various uncertainties of detection of the low energy events, especially the flavor identification, systematics, {\it etc.} Super-PINGU can be used simultaneously for the proton decay searches.