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

The experimental bound on lifetime of ν 3, the neutrino mass eigenstate with the smallest ν e component, is much weaker than those of ν 1 and ν 2 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 χ 2 analysis that the ν 3 lifetime divided by its mass, τ 3 /m 3, can be constrained to be τ 3 /m 3 > 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 ν 3 decay affects mass-ordering determination and precision measurements of the mixing parameters.