This review covers the modern era of experimental kaonic atom studies, encompassing 20 years of activity, defined by breakthroughs in technological developments which allowed performing a series of long-awaited precision measurements. Kaonic atoms are atomic systems where an electron is replaced by a negatively charged kaon, containing the strange quark, which interacts in the lowest orbits with the nucleus also by the strong interaction. As a result, their study offers the unique opportunity to perform experiments equivalent to scattering at vanishing relative energy. This allows one to study the strong interaction between the antikaon and the nucleon or the nucleus “at threshold,” namely, at zero relative energy, without the need of ad hoc extrapolation to zero energy, as in scattering experiments. The fast progress achieved in performing precision light kaonic atom experiments, which also solved long-pending inconsistencies with theoretical calculations generated by old measurements, relies on the development of novel cryogenic targets, x-ray detectors, and the availability of pure and intense charged kaon beams, which propelled an unprecedented progress in the field. Future experiments, based on new undergoing technological developments, will further boost the kaonic atom studies, thus fostering a deeper understanding of the low-energy strong interaction extended to the second family of quarks.

中文翻译：

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轻质钾离子原子实验的现代时代

这篇综述涵盖了实验性钾原子研究的现代时代，涵盖了20年的活动，这是由技术发展的突破所定义的，该技术允许进行一系列期待已久的精确测量。钾原子是一个原子系统，其中电子被带负电荷的钾取代，其中包含奇怪的夸克，该夸克在最弱的轨道上与原子核也通过强相互作用而相互作用。结果，他们的研究提供了独特的机会来进行相当于消失相对能量时的散射实验。这使人们能够研究“反阈”与核子或核“阈值”（即相对能量为零）之间的强相互作用，而无需特别的研究。外推至零能量，例如在散射实验中。在进行精密轻质钾原子实验方面取得的快速进展，也解决了长期以来与旧测量产生的理论计算不一致的问题，这取决于新型低温靶，X射线检测器的开发以及纯净和强电荷的钾离子的可用性光束，推动了该领域前所未有的进步。基于新技术的发展，未来的实验将进一步促进对钾原子的研究，从而加深对扩展至第二夸克族的低能强相互作用的理解。