Technische Universität Darmstadt, Fachbereich Physik, Darmstadt, Germany.
GSI Helmholtzzentrum für Schwerionenforschung GmbH, Darmstadt, Germany.
Nature. 2022 Jun;606(7915):678-682. doi: 10.1038/s41586-022-04827-6. Epub 2022 Jun 22.
A long-standing question in nuclear physics is whether chargeless nuclear systems can exist. To our knowledge, only neutron stars represent near-pure neutron systems, where neutrons are squeezed together by the gravitational force to very high densities. The experimental search for isolated multi-neutron systems has been an ongoing quest for several decades, with a particular focus on the four-neutron system called the tetraneutron, resulting in only a few indications of its existence so far, leaving the tetraneutron an elusive nuclear system for six decades. Here we report on the observation of a resonance-like structure near threshold in the four-neutron system that is consistent with a quasi-bound tetraneutron state existing for a very short time. The measured energy and width of this state provide a key benchmark for our understanding of the nuclear force. The use of an experimental approach based on a knockout reaction at large momentum transfer with a radioactive high-energy He beam was key.
长期以来，核物理学界一直存在一个问题，即不带电荷的核系统是否能够存在。据我们所知，只有中子星代表了近乎纯中子的系统，其中中子在引力的作用下被挤压到极高的密度。几十年来，人们一直在实验上寻找孤立的多中子系统，特别是寻找被称为四中子的四中子系统，目前为止只有少数几个存在的迹象，这使得四中子成为了一个难以捉摸的核系统长达六十年。在这里，我们报告了在四中子系统中在阈附近观察到的类似于共振的结构，这与存在极短时间的准束缚四中子态一致。该态的测量能量和宽度为我们理解核力提供了一个关键的基准。使用基于放射性高能氦束在大动量转移下的 knockout 反应的实验方法是关键。
