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

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.