Constraint on neutrino decay with medium-baseline reactor neutrino oscillation experiments

The experimental bound on lifetime of ν3, the neutrino mass eigenstate with the smallest νe component, is much weaker than those of ν1 and ν2 by many orders of magnitude to which the astrophysical constraints apply. We argue that the future reactor neutrino oscillation experiments with medium-baseline (∼50 km), such as JUNO or RENO-50, has the best chance of placing the most stringent constraint on ν3 lifetime among all neutrino experiments which utilize the artificial source neutrinos. Assuming decay into invisible states, we show by a detailed χ2 analysis that the ν3 lifetime divided by its mass, τ3/m3, can be constrained to be τ3/m3> 7.5 (5.5) × 10−11 s/eV at 95% (99%) C.L. by 100 kt·years exposure by JUNO. It may be further improved to the level comparable to the atmospheric neutrino bound by its longer run. We also discuss to what extent ν3 decay affects mass-ordering determination and precision measurements of the mixing parameters.