Terrestrial matter effects on reactor antineutrino oscillations at JUNO or RENO-50: how small is small?

TL;DR

This paper analyzes the small terrestrial matter effects on reactor antineutrino oscillations at JUNO and RENO-50, showing their impact on neutrino parameter measurements and the potential to detect these effects within a decade.

Contribution

It provides a detailed analytical and numerical assessment of terrestrial matter effects on reactor antineutrino experiments and estimates their detectability over time.

Findings

Terrestrial matter effects can reduce neutrino mass ordering sensitivity by ~0.6 in chi^2.

Neglecting matter effects may shift key neutrino parameters by 1 sigma.

A 2sigma detection of matter effects is possible within 10 years at JUNO.

Abstract

We have carefully examined, in both analytical and numerical ways, how small the terrestrial matter effects can be in a given medium-baseline reactor antineutrino oscillation experiment like JUNO or RENO-50. Taking the ongoing JUNO experiment for example, we show that the inclusion of terrestrial matter effects may reduce the sensitivity of the neutrino mass ordering measurement by \Delta \chi^2_{\rm MO} \simeq 0.6, and a neglect of such effects may shift the best-fit values of the flavor mixing angle \theta_{12} and the neutrino mass-squared difference \Delta_{21} by about 1\sigma to 2\sigma in the future data analysis. In addition, a preliminary estimate indicates that a 2\sigma sensitivity of establishing the terrestrial matter effects can be achieved for about 10 years of data taking at JUNO with the help of a proper near detector implementation.