Experimental study of decoherence effect at Daya Bay

The last unknown neutrino mixing angle has been successfully measured by the Daya Bay, RENO and Double Chooz experiments. The used oscillation probability formula is based on the plane-wave model. A wave-packet model is necessary for a self-consistent description of neutrino oscillations. The oscillation probability formula in the wave-packet model describes effects missing in the plane-wave approximation, such as delocalization, decoherence and dispersion which all depend on a single unknown parameter σ_p – momentum dispersion of the neutrino wave-packet. The survival probability formula in the wave-packet model was used to fit the Daya Bay data. The high-statistics data set of reactor ${\overline{\nu }}_e$ interactions in the Daya Bay experiment allows us to study the neutrino oscillation in the wave-packet model and provide the first experimental constraint of σ_p. Some results of our study are reported in this paper. (paper)