近日，STAR国际合作组取得一项新进展。他们实现了高能核碰撞中原子核的形状成像。相关研究成果已于2024年11月6日在国际权威学术期刊《自然》上发表。

本文介绍了一种集体流辅助的核形状成像方法，该方法通过以超相对论速度，碰撞原子核并分析射出碎片的集体响应，来成像原子核的整体形状。这项技术捕捉到了碰撞过程中，原子核内部物质空间分布的一个特定快照，该分布在流体动力学膨胀过程中，会在探测器观察到的粒子动量分布上留下印记。

研究人员在已知具有伸长、轴对称形状的基态铀-238核的碰撞中，对这种方法进行了基准测试。这项研究结果显示，在核基态中存在较大的变形，且略有偏离轴对称，这与之前的低能实验结果大致相符。这种方法为成像原子核形状提供了一种新途径，增强了他们对高能碰撞初始条件的理解，并解决了跨能量尺度核结构演化这一重要问题。

据悉，原子核是通过强核力在飞米尺度空间内自组织的、由多粒子组成的量子系统。这些复杂系统呈现出多种形状，传统上是通过低能非侵入性光谱技术来探索的。然而，在这些能量下，原子核的瞬时形状会被长时间尺度的量子涨落所掩盖，使得直接观察变得困难。

附：英文原文

Title: Imaging shapes of atomic nuclei in high-energy nuclear collisions

Author: STAR Collaboration

Issue&Volume: 2024-11-06

Abstract: Atomic nuclei are self-organized, many-body quantum systems bound by strong nuclear forces within femtometre-scale space. These complex systems manifest a variety of shapes, traditionally explored using non-invasive spectroscopic techniques at low energies. However, at these energies, their instantaneous shapes are obscured by long-timescale quantum fluctuations, making direct observation challenging. Here we introduce the collective-flow-assisted nuclear shape-imaging method, which images the nuclear global shape by colliding them at ultrarelativistic speeds and analysing the collective response of outgoing debris. This technique captures a collision-specific snapshot of the spatial matter distribution within the nuclei, which, through the hydrodynamic expansion, imprints patterns on the particle momentum distribution observed in detectors. We benchmark this method in collisions of ground-state uranium-238 nuclei, known for their elongated, axial-symmetric shape. Our findings show a large deformation with a slight deviation from axial symmetry in the nuclear ground state, aligning broadly with previous low-energy experiments. This approach offers a new method for imaging nuclear shapes, enhances our understanding of the initial conditions in high-energy collisions and addresses the important issue of nuclear structure evolution across energy scales.

DOI: 10.1038/s41586-024-08097-2

Source: https://www.nature.com/articles/s41586-024-08097-2