Exploring the Earth matter effect with atmospheric neutrinos in ice

TL;DR

This paper investigates how atmospheric neutrino observations in ice detectors like IceCube and PINGU can be used to perform neutrino oscillation tomography and determine the neutrino mass hierarchy by analyzing matter effects during neutrino propagation through Earth.

Contribution

It demonstrates the potential of current and future ice-based neutrino detectors to measure Earth's density fluctuations and determine neutrino mass hierarchy with high confidence within a few years.

Findings

DeepCore can detect ~10% Earth's density fluctuations after 10 years.

PINGU configurations can measure ~2-3% density fluctuations at 2 sigma after 10 years.

Hierarchy determination can reach 5 sigma confidence in 1-5 years depending on the detector.

Abstract

We study the possibility to perform neutrino oscillation tomography and to determine the neutrino mass hierarchy in kilometer-scale ice Cerenkov detectors by means of the theta13-driven matter effects which occur during the propagation of atmospheric neutrinos deep through the Earth. We consider the ongoing IceCube/DeepCore neutrino observatory and future planned extensions, such as the PINGU detector, which has a lower energy threshold. Our simulations include the impact of marginalization over the neutrino oscillation parameters and a fully correlated systematic uncertainty on the total number of events. For the current best-fit value of the mixing angle theta13, the DeepCore detector, due to its relatively high-energy threshold, could only be sensitive to fluctuations on the normalization of the Earth's density of \Delta\rho \simeq \pm 10% at ~ 1.6 sigma CL after 10 years in the case of a true normal hierarchy. For the two PINGU configurations we consider, overall density fluctuations of \Delta\rho \simeq \pm 3% (\pm 2%) could be measured at the 2 sigma CL after 10 years, also in the case of a normal mass hierarchy. We also compare the prospects to determine the neutrino mass hierarchy in these three configurations and find that this could be achieved at the 5 sigma CL, for both hierarchies, after 5 years in DeepCore and about 1 year in PINGU. This clearly shows the importance of lowering the energy threshold below 10 GeV so that detectors are fully sensitive to the resonant matter effects.