Reactor Antineutrino Spectrum Prediction At Jiangmen Underground Neutrino Observation

Neutrino physics is a cross-disciplinary research hotspot that encompasses high-energy physics,astrophysics,and cosmology.The oscillation mixing angle θ13 measured by the Daya Bay experiment is much larger than expected,greatly reducing the difficulty of determining the neutrino mass ordering by measuring the reactor antineutrino spectra.The Jiangmen underground neutrino observatory(Jiangmen Underground Neutrino Observatory,JUNO)is a new generation reactor neutrino experiment led by China.Its main physics goals are to determine the neutrino mass ordering and to accurately measure the parameters of neutrino oscillations,while also making contributions supernova neutrinos,solar neutrinos,and atmospheric neutrinos.JUNO will determine the neutrino mass ordering by precisely measuring reactor antineutrino spectrum,and expected spectra are input as references when analyzing spectra.The expected reactor neutrino spectrum can be theoretically calculated using nuclear fission neutrino pectra,the baseline of the reactor,reactor-related physical quantities,and detector-related parameters.However,errors exist in the input physical quantities,which ultimately manifest as errors in the expected spectrum.The Taishan antineutrino observatory(Taishan Antineutrino Observatory,TAO)is the near-site detection experiment of JUNO,and one of its physics goals is to accurately measure the reactor neutrino spectrum and provide a reference spectrum for JUNO.The distance between the TAO detector and the reactor is approximately 30 m,and the size of the reactor core is about 4 m.At this distance,the size of the core may distort the shape of the spectrum and also have an impact on the fine structure of the reactor neutrino spectrum.Therefore,it is necessary to conduct in-depth research on the influence of reactor geometry effects on the reactor neutrino spectrum.This article addresses two issues and conducts the following work:(1)calculates the expected neutrino spectrum and total neutrino spectrum for each reactor in JUNO based on the neutrino spectra in nuclear fission,reactor baselines,neutrino oscillation probabilities,and relevant physical quantities of reactors and detectors;(2)evaluates the contribution of errors in each physical quantity to the expected spectrum error through theoretical calculations and Monte Carlo simulations,taking into account the error and correlation of each input physical quantity.The results show that errors of neutrino spectrum from nuclear fission neutrino spectra and neutrino oscillation probabilities are larger,the error of spectrum introduced by oscillation mainly come from the error of θ12,m212 and m322.(3)examines the impact of reactor geometry effects and uncertainty in core power distribution on the neutrino spectrum by establishing both a volumetric neutrino source model and a point neutrino source model for the core.The results show that the reactor geometry effect has a negligible impact on the neutrino flux strength,and the impact on the spectrum shape is in the order of 10-6.