Abstract
The disappearance of reactor bar{nu }_e observed by the Daya Bay experiment is examined in the framework of a model in which the neutrino is described by a wave packet with a relative intrinsic momentum dispersion sigma _mathrm{{rel}}. Three pairs of nuclear reactors and eight antineutrino detectors, each with good energy resolution, distributed among three experimental halls, supply a high-statistics sample of bar{nu }_e acquired at nine different baselines. This provides a unique platform to test the effects which arise from the wave packet treatment of neutrino oscillation. The modified survival probability formula was used to fit Daya Bay data, providing the first experimental limits: 2.38 times 10^{-17}< sigma _mathrm{{rel}} < 0.23. Treating the dimensions of the reactor cores and detectors as constraints, the limits are improved: 10^{-14} lesssim sigma _text {rel} < 0.23, and an upper limit of sigma _text {rel}<0.20 (which corresponds to sigma _x gtrsim 10^{-11},mathrm{{cm }}) is obtained. All limits correspond to a 95% C.L. Furthermore, the effect due to the wave packet nature of neutrino oscillation is found to be insignificant for reactor antineutrinos detected by the Daya Bay experiment thus ensuring an unbiased measurement of the oscillation parameters sin ^22theta _{13} and varDelta m^2_{32} within the plane wave model.
Highlights
Daya Bay experiment is examined in the framework of a model in which the neutrino is described by a wave packet with a relative intrinsic momentum dispersion σrel
The effect due to the wave packet nature of neutrino oscillation is found to be insignificant for reactor antineutrinos detected by the Daya Bay experiment ensuring an unbiased measurement of the oscillation parameters sin2
We performed a search for the footprint of the neutrino wave packet which should show itself through specific modifications of the neutrino oscillation probability
Summary
The wave packet is a coherent superposition of different waves whose momenta are distributed around the most probable value, with a certain “width” or dispersion. The wave packet formalism facilitates the resolution of the paradoxes of the plane wave theory, and predicts the existence of a coherence length The latter arises due to the different group velocities of a pair νk and ν j , which causes a separation in space over time. The day–night asymmetry of solar neutrinos provides an evidence that solar neutrinos come to the Earth in an incoherent mixture [44] These data do not provide any quantitative information about the size of a neutrino wave packet because of an averaging over the large volume of the Sun. One of the motivations of this paper is to provide the first quantitative study of a possible loss of coherence in the quantum state of neutrinos following the wave packet treatment of neutrino oscillations, using data from the Daya Bay Reactor Neutrino Experiment. The large statistics, good energy resolution, and multiple baselines of the Daya Bay experiment make its data valuable in the study of these quantum decoherence effects in neutrino oscillation
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