Neutrino Decoherence and the Mass Hierarchy in the JUNO Experiment

TL;DR

This paper investigates how neutrino wavepacket size and decoherence influence JUNO's ability to determine the neutrino mass hierarchy, revealing that wavepacket effects can significantly impact hierarchy sensitivity.

Contribution

It analyzes the impact of finite neutrino wavepacket size on JUNO's hierarchy determination and explores the interplay between decoherence effects and experimental sensitivity.

Findings

Wavepacket effects can hinder hierarchy determination up to two orders of magnitude above current limits.

JUNO's high statistics and energy resolution make it sensitive to wavepacket size and decoherence effects.

The study discusses potential future improvements in sensitivity through additional measurements.

Abstract

The finite size of a neutrino wavepacket at creation can affect its oscillation probability. Here, we consider the electron antineutrino wavepacket and decoherence in the context of the nuclear reactor based experiment JUNO. Given JUNO's high expected statistics [$\sim$100k IBD events ($\bar{\nu}_e p \rightarrow e^+ n$)], long baseline ($\sim$53\,km), and excellent energy resolution [$\sim$$0.03/\sqrt{E_{\mathrm{vis}}~\mathrm{(MeV)}}$], its sensitivity to the size of the wavepacket is expected to be quite strong. Unfortunately, this sensitivity may weaken the experiment's ability to measure the orientation of the neutrino mass hierarchy for currently allowed values of the wavepacket size. Here, we report both the JUNO experiment's ability to determine the hierarchy orientation in the presence of a finite wavepacket and its simultaneous sensitivity to size of the wavepacket and the hierarchy. We find that wavepacket effects are relevant for the hierarchy determination up to nearly two orders of magnitude above the current experimental lower limit on the size, noting that there is no theoretical consensus on the expectation of this value. We also consider the effect in the context of other aspects of JUNO's nominal three-neutrino oscillation measurement physics program and the prospect of future enhancements to sensitivity, including from precise measurements of $\Delta m^2_{3l}$ and a near detector.