The weak magnetism correction and its uncertainty to nuclear beta-decay play a major role in determining the significance of the reactor neutrino anomaly. Here we examine the common approximation used for one-body weak magnetism in the calculation of fission antineutrino spectra, wherein matrix elements of the orbital angular momentum operator contribution to the magnetic dipole current are assumed to be proportional to those of the spin operator. Although we find this approximation invalid for a large set of nuclear structure situations, we conclude that it is valid for the relevant allowed beta-decays between fission fragments. In particular, the uncertainty in the fission antineutrino due to the uncertainty in the one-body weak magnetism correction is found to be less than 1%. Thus, the dominant uncertainty from weak magnetism for reactor neutrino fluxes lies in the uncertainty in the two-body meson-exchange magnetic dipole current.
First \textit{ab initio} calculations of first-forbidden $β$ transitions in the reactor antineutrino anomaly
Peking University（北京大学）；School of Physics, and State Key Laboratory of Nuclear Physics and Technology, Peking University（北京大学物理学院，核物理与技术国家重点实验室）；Institute of Modern Physics, Fudan University（复旦大学现代物理研究所）；Shanghai Research Center for Theoretical Nuclear Physics, NSFC and Fudan University（上海理论核物理研究中心，NSFC和复旦大学）；Southern Center for Nuclear-Science Theory, Institute of Modern Physics, Chinese Academy of Sciences（中国科学院现代物理研究所南方核科学理论中心）
New fissile isotopes antineutrino spectra ($^{235}$U, $^{238}$U, $^{239}$Pu and $^{241}$Pu) calculation is presented. On base of summation method the toy model was developed. It was shown that total antineutrino number is conserved in framework of given database on individual fragments yields. The analysis of antineutrino spectrum shape says that any presented antineutrino spectrum should satisfy to the total antineutrino number conservation.
Model-independent reactor isotopic cross sections per fission are determined by global fits of the reactor antineutrino data from High-Enriched Uranium (HEU) reactor rates, Low-Enriched Uranium (LEU) reactor rates, and reactor fuel evolution data. Taking account of the implicit quasi-linear relationship between the fission fractions of $^{239}\rm{Pu}$ and $^{241}\rm{Pu}$ in the LEU reactor data, the Inverse-Beta-Decay (IBD) yields and their correlations of the fissionable isotopes $^{235}\rm{U}$, $^{238}\rm{U}$, and Pu's are obtained. The data-driven isotopic IBD yields provide an anomaly-free…
We present results from global fits to the available reactor antineutrino dataset, as of Fall 2019, to determine the global preference for a fourth, sterile neutrino. We have separately considered experiments that measure the integrated inverse-beta decay (IBD) rate from those that measure the energy spectrum of IBD events at one or more locations. The software used is the newly developed GLoBESfit tool set which is based on the publicly available GLoBES framework and will be released as open-source software.
We report a reanalysis of the reactor antineutrino energy spectra based on the new relative measurements of the ratio $R=\!^{e}S_5/^{e}S_9$ between cumulative $β$ spectra from $^{235}$U and $^{239}$Pu, performed at a research reactor in National Research Centre Kurchatov Institute (KI). A discrepancy with the $β$ spectra measured at Institut Laue-Langevin (ILL) was observed, indicating a steady excess of the ILL ratio by the factor of $1.054\pm0.002$. We find a value of the ratio between inverse beta decay cross section per fission for $^{235}$U and $^{239}$Pu: $(^5σ_f/^9σ_f)_{KI} = 1.45 \pm 0…
New \textit{ab initio} calculations of the isotopic reactor antineutrino fluxes are provided with exact numerical calculations of the lepton wave functions, assuming all the decay branches are allowed GT transitions. We illustrate that the analytical Fermi function and finite size effect each could have the largest spectral deviation of $\mathcal{O}(10\%)$, whereas the effect of their combination could result in spectral deviations at the level of 5%-10%. Meanwhile, we also find that several forms of the extended charge distributions have negligible effects on the spectral variation. Using the…
Particle physics origin of the 5 MeV bump in the reactor antineutrino spectrum?
中微子物理学中最令人困惑的问题之一是反应堆反中微子光谱中5 MeV过量的起源。本文研究了有机闪烁体探测器中通过反应$^{13}$ C $(\overlineν, \overlineν^\prime n)^{12}$ C $^*$产生的过量。$^{12}$ C $^*$的去激发产生瞬发$4.4$ MeV光子，而产物中子的热化引起质子反冲，这又产生具有有限宽度的额外瞬发能量贡献。这些效应可以共同模拟能量约为5 MeV的逆β衰变事件。我们考虑了几个非标准中微子相互作用产生这样一个过程，并发现大亚湾首选的参数空间是不利的中微子诱导氘衰变和相干弹性中微子核散射的测量。虽然非最小粒子物理方案可能是可行的，但这种异常的核物理解决方案似乎更有吸引力。
Theory of inverse beta decay for reactor antineutrinos
Institute of Theoretical Physics, Chinese Academy of Sciences（中国科学院理论物理研究所）；Institute of High Energy Physics, Chinese Academy of Sciences（中国科学院高能物理研究所）；China Center of Advanced Science and Technology（中国高等科学技术中心）
In this work, we present an analysis of the sensitivity to the active-sterile neutrino mixing with the Indian Scintillator Matrix for Reactor Anti-Neutrino (ISMRAN) experimental set-up at very short baseline. In this article, we have considered the measurement of electron antineutrino induced events employing a single detector which can be placed either at a single position or moved between near and far positions from the given reactor core. Results extracted in the later case are independent of the theoretical prediction of the reactor anti-neutrino spectrum and detector related systematic un…
