This article reports the measurement of the ²³⁵U-induced antineutrino spectrum shape by the Stereo experiment. 43 000 antineutrinos have been detected at about 10m from the highly enriched core of the ILL reactor during 118 full days equivalent at nominal power. The measured inverse beta decay spectrum is unfolded to provide a pure ²³⁵U spectrum in antineutrino energy. A careful study of the unfolding procedure, including a cross-validation by an independent framework, has shown that no major biases are introduced by the method. A significant local distortion is found with respect to predictions around E _ν ≃ 5.3 MeV. A Gaussian fit of this local excess leads to an amplitude of A = 12.1 3.4% (3.5σ).

本文报道了立体实验对²³⁵ U 诱导的反中微子谱形状的测量。在相当于标称功率的 118 天期间，在距 ILL 反应堆高浓缩堆芯约 10m 处检测到 43 000 个反中微子。测得的逆贝塔衰变谱被展开以提供一个纯²³⁵ U 的反中微子能量谱。对展开过程的仔细研究，包括由独立框架进行的交叉验证，表明该方法没有引入重大偏差。在E _ν ≃ 5.3 MeV附近的预测中发现了显着的局部失真。这种局部过量的高斯拟合导致振幅A = 12.1 3.4% (3.5 σ )。