Probing unitarity violation of lepton flavor mixing matrix with reactor antineutrinos at JUNO and TAO

Abstract

Motivated by the precise measurements of neutrino oscillation parameters at Jiangmen Underground Neutrino Observatory (JUNO), we investigate the possibility of probing the unitarity violation of lepton flavor mixing matrix solely with reactor antineutrinos. First, we stress that it is necessary to reconsider the production and detection of neutrinos in a self-consistent way, apart from neutrino propagation, when analyzing experimental sensitivities to unitarity violation. Then, concentrating on JUNO and its satellite experiment Taishan Antineutrino Observatory (TAO), we demonstrate how the event rates of inverse beta decays (i.e., $\overline{\nu}^{}_e + p \to e^+ + n$) for observing $\overline{\nu}^{}_e \to \overline{\nu}^{}_e$ oscillations, and those of elastic antineutrino-electron scattering (i.e., $\overline{\nu}^{}_\alpha + e^- \to \overline{\nu}^{}_\alpha + e^-$ with $\alpha = e, \mu, \tau$) for $\overline{\nu}^{}_e \to \overline{\nu}^{}_\mu$ and $\overline{\nu}^{}_e \to \overline{\nu}^{}_\tau$ oscillations, depend on the parameters characterizing unitarity violation. Our investigation will be useful for JUNO and TAO to place independent constraints with more data in the near future.