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.

Comments: PDFLatex, 14 figures. Discussion of effects of the systematic errors and flavor misidentification on sensitivity to the CP phase expanded; role of uncertainties in the 2 - 3 mixing explored. 3 new figures added