IceCube Measures Cosmic Ray Neutrino Flavor Ratios

The IceCube experiment released a preprint last week giving the results of a study of the neutrino flavor ratios for high energy cosmic ray neutrinos. Approximately equal numbers of each of the three flavors are expected, and this is consistent with what is seen if the neutrinos are assumed to originate largely from pion decay and oscillate given the current best fit oscillation parameters.

To do this measurement, IceCube classifies events as “track like” (muons) or “shower like” (electrons and also taus) and uses this to calculate an exclusion region in the space of neutrino flavor ratios. While the result does exclude some regions at the 2σ (~95%) level, it is clearly too limited by statistics at this time to really hope to pin down the actual flavor ratios.