Nature. 2023 Feb;614(7947):244-248. doi: 10.1038/s41586-022-05557-5. Epub 2023 Jan 18.
Notwithstanding decades of progress since Yukawa first developed a description of the force between nucleons in terms of meson exchange, a full understanding of the strong interaction remains a considerable challenge in modern science. One remaining difficulty arises from the non-perturbative nature of the strong force, which leads to the phenomenon of quark confinement at distances on the order of the size of the proton. Here we show that, in relativistic heavy-ion collisions, in which quarks and gluons are set free over an extended volume, two species of produced vector (spin-1) mesons, namely ϕ and K, emerge with a surprising pattern of global spin alignment. In particular, the global spin alignment for ϕ is unexpectedly large, whereas that for K is consistent with zero. The observed spin-alignment pattern and magnitude for ϕ cannot be explained by conventional mechanisms, whereas a model with a connection to strong force fields, that is, an effective proxy description within the standard model and quantum chromodynamics, accommodates the current data. This connection, if fully established, will open a potential new avenue for studying the behaviour of strong force fields.
尽管自 Yukawa 首次用介子交换描述核子之间的力以来已经过去了几十年，但要完全理解强相互作用仍然是现代科学的一个重大挑战。一个仍然存在的困难源于强相互作用的非微扰性质，这导致在质子大小的距离上出现夸克禁闭现象。在这里，我们表明，在相对论重离子碰撞中，夸克和胶子在扩展的体积中被释放出来，两种产生的矢量（自旋-1）介子，即 ϕ 和 K，以一种令人惊讶的整体自旋排列模式出现。特别是，ϕ 的整体自旋排列出乎意料地大，而 K 的则与零一致。观察到的 ϕ 的自旋排列模式和幅度不能用传统机制来解释，而与强力场有联系的模型，即在标准模型和量子色动力学中的有效代理描述，可以容纳当前的数据。如果这种联系得到充分确立，将为研究强力场的行为开辟一条潜在的新途径。
