Establishing Earth's Matter Effect in Atmospheric Neutrino Oscillations at IceCube DeepCore

TL;DR

This work addresses the challenge of observing Earth's matter effects in atmospheric neutrino oscillations within a three-flavor framework by exploiting the recently established sensitivity from the IceCube DeepCore detector. It employs a 9.3-year-equivalent Monte Carlo dataset, with a CNN-based particle ID and careful treatment of systematics, to perform an Asimov sensitivity test against the PREM density profile while comparing normal and inverted mass orderings. The results show modest but robust discrimination between vacuum and matter scenarios (e.g., $1.57\sigma$ for NO and $1.10\sigma$ for IO at $\theta_{23}=47.5^{\circ}$), and project roughly a threefold improvement with the IceCube Upgrade. Overall, the study demonstrates a viable path to detecting Earth matter effects with atmospheric neutrinos and highlights the potential for enhanced sensitivity with lower energy thresholds and improved systematics, informing future oscillation and mass-ordering investigations.

Abstract

The discovery of the non-zero value of $θ_{13}$ has opened an exciting opportunity to probe the Earth's matter effects in three-flavor oscillations of atmospheric neutrinos. These matter effects depend on both neutrino energy and the electron density distributions encountered during their propagation through Earth. In this contribution, we present preliminary sensitivities from the DeepCore detector, a densely instrumented sub-array of the IceCube neutrino observatory at the South Pole, demonstrating its ability to observe these matter effects in atmospheric neutrino oscillations. Using simulated data equivalent to 9.3 years of observations at IceCube DeepCore, we show the sensitivity of the DeepCore to reject the vacuum oscillation hypothesis and align with the Preliminary Reference Earth Model. Additionally, we present the expected improvement in sensitivity for rejecting the vacuum oscillations using the upcoming IceCube Upgrade, a low-energy extension of the IceCube detector.

Figures (1)

• Figure 1: Asimov sensitivity as a function of the true value of $\sin^2\theta_{23}$ to establish the Earth's matter effects in atmospheric neutrino oscillations. The left panel shows the expected sensitivity based on IceCube DeepCore simulated data, equivalent to 9.3 years of observations, while the right panel presents the expected sensitivity using the current DeepCore setup only (dashed line) and with the Upgrade included along with DeepCore (solid line).