Phys. Rev. D 88, 013013 (2013)

Buried deep in Antarctica is the neutrino observatory known as IceCube: more than 5,000 basketball-size 'digital optical modules' (DOMs) threaded through a cubic kilometre of ice. IceCube collects signals created in the ice by high-energy neutrinos from astrophysical sources — and has recently reported the detection of a couple of neutrinos at PeV energies, the highest energies observed so far.

But plans are afoot to equip IceCube for detection of atmospheric neutrinos at much lower energies, by upping the density of DOMs in just a small sub-volume of the existing detector. The first stage would be 'DeepCore', which could be followed by a second stage called 'Precision IceCube Next Generation Upgrade' — PINGU.

And, Walter Winter proposes, PINGU could provide data to determine the neutrino mass hierarchy: although neutrinos are known to have mass and the differences between their squared mass values are also measured, the order of the mass eigenstates is still a mystery. The operation of PINGU over three years could, reckons Winter, establish the hierarchy at least at the 90% confidence level or even up to as much as four-sigma.