For the inelastic electron scattering of atoms and molecules, a consensus has been reached that the first Born approximation is easily approached by decreasing the momentum transfer at the same impact electron energy or increasing the impact electron energy at the same momentum transfer. Although this consensus is applicable for the elastic electron scattering of most atoms and molecules, it is violated for helium where the experimental differential cross sections deviate from the first Born approximation prediction gradually with the decrease of squared momentum transfer at the same impact electron energy. Since this anomalous phenomenon was observed more than 40 years ago, the intrinsic mechanism is not explicit. In the present work, using the high-resolution x-ray scattering, we isolate the scattering contribution from the nucleus and directly obtain the pure electronic structure of helium. Then, the anomalous asymptotic behavior of the elastic electron scattering of helium has been elucidated, i.e., in the small squared momentum transfer region, the scattering contribution from the target's electrons is counteracted by the one from the atomic nucleus, which results in the residual contribution beyond the first Born approximation being drastically enlarged.

中文翻译：

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氦弹性电子散射的异常渐近行为研究。

对于原子和分子的非弹性电子散射，已经达成共识，可以通过在相同的冲击电子能量下降低动量传递或在相同的动量传递下增加冲击电子能量来轻松地接近第一个玻恩近似。尽管此共识适用于大多数原子和分子的弹性电子散射，但对于氦气却违反了这一点，氦气的实验微分截面逐渐偏离第一波恩近似预测，并且在相同的冲击电子能量下平方动量传递逐渐减小。由于这种异常现象是在40多年前观察到的，其内在机制尚不清楚。在目前的工作中，使用高分辨率X射线散射，我们从原子核中分离出散射贡献，并直接获得氦的纯电子结构。然后，阐明了氦的弹性电子散射的异常渐近行为，即在小平方动量传递区域中，目标电子的散射贡献被原子核中的一个抵消，这导致了残余贡献超出了第一个Born近似值的急剧扩大。