[论文解读] Isotope shift, non-linearity of King plot and search for nuclear island of stability and new particles

V. V. Flambaum, Amy Geddes+1 more|arXiv (Cornell University)|Sep 2, 2017

Atomic and Subatomic Physics Research被引用 2

一句话总结

本文推导出适用于任意电子角动量的相对论性单粒子同位素位移公式，可估算超重元素与位于幻数壳层（N=184）附近的核素之间的跃迁频率差异。研究发现，核极化率导致King图出现显著非线性，该非线性可被用于测量核极化率的变化，并通过Yukawa型相互作用探测新粒子。

ABSTRACT

The Racah-Rosenthal-Breit formula describes the isotope field shift for s-wave only and is not valid in heavy atoms where the relativistic effects are important. We derive a single-particle relativistic formula for the isotope shift for an arbitrary electron angular momentum; we then apply it to estimate the differences in the transition frequencies between the superheavy atoms produced in laboratory and atoms with nuclei belonging to the hypothetical island of stability (these nuclei have a magical number of neutrons N=184). Our results may be applied to the search for metastable neutron-rich isotopes in astrophysical atomic spectra using the known values of the transition frequencies for the neutron deficient isotopes produced in laboratory. An example may be the spectra of the Przybylski's star where superheavy elements up to Z=99 have been possibly identified. We have found that the nuclear polarizability contribution leads to the significant deviation of the King plot for isotope shifts from the linearity. Therefore, the measurements of the non-linearity of King plots may be applied to measure the nuclear polarizability change between individual isotopes. It was recently suggested that such measurements may also be used to search for new particles mediating Yukawa-type interactions in atoms. We estimate the non-linear corrections to the King plot including contributions of the relativistic effects in the field shift, isotope shift due to the nuclear polarizability, many-body effects and effect of hypothetical new particles. Our estimates provide theoretical limitations on the sensitivity of such a search and should help in selection of the most suitable atoms for corresponding experiments.

研究动机与目标

• 推导适用于具有任意电子角动量的重原子的相对论性同位素位移公式。
• 估算超重元素与接近幻数壳层（N=184）的核素之间的跃迁频率差异。
• 研究核极化率如何导致King图线性关系的偏离，以及该偏离是否可用于测量极化率的变化。
• 评估King图非线性作为探测通过Yukawa型相互作用传播的新粒子的潜力。
• 为实验中寻找标准模型之外的新物理提供理论约束，以选择最优原子体系。

提出的方法

• 推导适用于任意电子角动量量子数的单粒子相对论性同位素位移公式。
• 将该公式应用于Z≤99的超重元素，特别比较实验室中产生的缺中子同位素与N=184附近假设的富中子同位素之间的同位素位移。
• 纳入相对论效应、场移项、核极化率、多体效应以及假设新粒子的贡献。
• 对由于这些贡献（尤其是核极化率）引起的King图非线性偏差进行建模。
• 利用已知的缺中子同位素的跃迁频率，预测富中子同位素的位移，尤其关注天体物理观测的相关性。

实验结果

研究问题

• RQ1 相对论效应如何影响具有任意电子角动量的超重元素的同位素位移？
• RQ2 核极化率在多大程度上导致同位素位移的King图出现非线性？
• RQ3 King图中的非线性是否可用于测量同位素间核极化率的变化？
• RQ4 King图非线性对通过Yukawa型相互作用传播的新粒子的理论灵敏度如何？
• RQ5 哪些原子体系最适于通过同位素位移测量探测此类新物理？

主要发现

• 推导出的相对论性同位素位移公式将Racah-Rosenthal-Breit公式的适用范围扩展至具有显著相对论效应的重原子。
• 核极化率对King图的非线性贡献显著，尤其在超重元素中更为明显。
• King图中的非线性可作为同位素间核极化率变化的可观测量代理。
• 包含相对论效应、多体修正以及假设新粒子后，King图曲率的预期值发生改变。
• 该模型为同位素位移实验探测新粒子的灵敏度提供了理论上限，有助于未来筛选最优原子候选体系。