Abstract
The Jiangmen Underground Neutrino Observatory (JUNO) project aims at probing, at the same time, the two main frequencies of three-flavor neutrino oscillations, as well as their interference related to the mass ordering (normal or inverted), at a distance of ~53 km from two powerful reactor complexes in China, at Yangjiang and Taishan. In the latter complex, the unoscillated spectrum from one reactor core is planned to be closely monitored by the Taishan Antineutrino Observatory (TAO), expected to have better resolution (x 1/2) and higher statistics (x 30) than JUNO. In the context of neutrino energy spectra endowed with fine-structure features from summation calculations, we analyze in detail the effects of energy resolution and nucleon recoil on observable event spectra. We show that a model spectrum in TAO can be mapped into a corresponding spectrum in JUNO through appropriate convolutions. The mapping is exact in the hypothetical case without oscillations, and holds to a very good accuracy in the real case with oscillations. We then analyze the sensitivity to mass ordering of JUNO (and its precision oscillometry capabilities) assuming a single reference spectrum, as well as bundles of variant spectra, as obtained by changing nuclear input uncertainties in summation calculations from a publicly available toolkit. We show through a chi-squared analysis that variant spectra induce little reduction of the sensitivity in JUNO, especially when TAO constraints are included. Subtle aspects of the statistical analysis of variant spectra are also discussed.
Highlights
Experiments based on electron antineutrinos from nuclear reactors—referred to as reactor neutrinos hereafter—have marked the history of neutrino physics [1,2,3,4,5]
The next-generation, medium baseline reactor neutrino experiment Jiangmen Underground Neutrino Observatory (JUNO) is planned to probe the full pattern of νe disappearance for L=E ∼ ðfew MeVÞ= ð53 kmÞ, including the precision measurements of oscillations induced by the ðδm2; θ12Þ and ðΔm2; θ13Þ massmixing pairs, and their interference effects governed by the neutrino mass ordering, namely, signðδm2=Δm2Þ
We have studied the relations between the observable event spectra in Taishan Antineutrino Observatory (TAO) (ST) and JUNO (SJ), in the simplifying assumption that they are generated by the same unobservable neutrino spectrum (Sν), including finestructure features as emerging in summation calculations
Summary
Experiments based on electron antineutrinos (νe) from nuclear reactors—referred to as reactor neutrinos hereafter—have marked the history of neutrino physics [1,2,3,4,5]. Observing or constraining (at least a few) prominent substructures in future, highresolution and high-statistics reactor neutrino experiments, would be beneficial both for nuclear spectroscopy (allowing to pin down the spectral contributions of specific fission products [57]), and for neutrino oscillometry (reducing small-scale fuzzy uncertainties that might affect the JUNO sensitivity to mass ordering [58]). The latter benefit may be marginal if one assumes “known” substructures from nuclear databases [59,60], the observation of unexpected spectral anomalies at large energy scales (normalization and bump issues) provides a warning about the possible emergence of “unknown” features at small scales.
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