Neutrino decoherence and the mass hierarchy in the JUNO experiment

Abstract

The finite size of a neutrino wave packet at creation can affect its oscillation probability. Here, we consider the electron antineutrino wave packet and decoherence in the context of the nuclear reactor-based experiment JUNO. Given JUNO's high expected statistics [$\ensuremath{\sim}100\mathrm{k}$ IBD events (${\overline{\ensuremath{\nu}}}_{e}p\ensuremath{\rightarrow}{e}^{+}n$)], long baseline ($\ensuremath{\sim}53\text{ }\text{ }\mathrm{km}$), and excellent energy resolution [$\ensuremath{\sim}0.03/\sqrt{{E}_{\mathrm{vis}}(\mathrm{MeV})}$], its sensitivity to the size of the wave packet 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 wave-packet size. Here, we report both the JUNO experiment's ability to determine the hierarchy orientation in the presence of a finite wave packet and its simultaneous sensitivity to size of the wave packet and the hierarchy. We find that wave-packet 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 $\mathrm{\ensuremath{\Delta}}{m}_{3l}^{2}$ and a near detector.