When a muon neutrino crashes into the ice, it sometimes produces a hadronic shower and a muon, which are then detected by one of the 5,000 sensors of the IceCube Neutrino Observatory. This hadronic shower carries a fraction of the energy of the original neutrino. This fraction is described by a parameter known as inelasticity. Understanding the distribution of inelasticity of neutrino interactions provides another way of uncovering unique physics that could challenge the Standard Model, which physicists use to explain the fundamental particles in the universe.
In particle physics, a quantity called cross section is used to describe the probability that a particle interacts with matter. For IceCube, it is the probability that a neutrino interacts with a nucleon, a subatomic particle in the nucleus of an atom. Cross section is a multidimensional quantity with inelasticity commonly used as one of its dimensions. Inelasticity distribution measurements are a type of cross section measurement and are key to understanding the unique physics surrounding neutrinos.
Previously, the IceCube Collaboration presented its first measurements of the neutrino inelasticity at very high energies (1 TeV up to nearly 800 TeV), which were found to be in good agreement with Standard Model predictions and were later used to perform other measurements. In a new study submitted to Physical Review D, the IceCube Collaboration presents measurements of the neutrino inelasticity distribution in the 80–560 GeV energy range, a region where such measurements did not exist. These measurements are in agreement with existing cross section models where accelerator data is not available.
For the analysis, researchers used nine years of data taken from the low-energy extension, IceCube DeepCore, located at the bottom, central region of IceCube. Because in some cases neutrino-nucleon interactions leave behind a hadronic shower (cascade) and muon (track) in the detector, researchers are able to estimate the neutrino inelasticity using the reconstructed total neutrino energy.
Using an approach that separates the energies for the track and cascade, a ratio of the cascade energy to the total energy was calculated to measure inelasticity. The high-purity (99%) sample of muon-neutrino charged current interactions was used to measure the inelasticity distribution in three energy ranges where mean inelasticity was used to describe the shapes of the distributions.
“We compared our mean inelasticity results to predictions based on existing cross section and flux models and found that all flux and cross section combinations are in agreement with our measurements,” says Maria Liubarska, a PhD student at the University of Alberta in Canada and study lead. “This result validates theoretical predictions, which are used as input for other IceCube measurements in the energy range of 80-560 GeV.”
Although the data does not yet exclude any of the existing models, the precision of the measurements will only improve with more data collection and improvement to detector calibration thanks to the nearly finished IceCube Upgrade project.
+ info “Measurement of the inelasticity distribution of neutrino-nucleon interactions for 80 GeV < Eν < 560 GeV with IceCube DeepCore,” IceCube Collaboration: R. Abbasi et al. Submitted to Physical Review D. arxiv.org/abs/2502.13299