Vol.35,

With the advancement of accelerator technology, it became possible to generate ion beams of various naturally occurring nuclides in ion sources and accelerate them to very high energies. Heavy-ion physics emerged as a critical frontier in nuclear science, with countries like the United States, the Soviet Union, and France competing to synthesize new nuclides and elements using heavy-ion beams, thereby sparking a global race. Besides traditional reactions such as elastic scattering, direct reactions, and compound nuclear reactions, various new types of nuclear reactions were discovered with heavy-ion beams. Heavy-ion beams also found widespread applications in fields such as material irradiation, nuclear agriculture, and nuclear medicine. In the 1970s, IMP converted its 1.5-meter light ion cyclotron into a heavy-ion accelerator, marking the beginning of China's efforts to catch up with global research at the forefront of nuclear physics. Professor Wenqing Shen successively served as the group leader of the first experimental nuclear physics division and as the deputy director of the second division, responsible for leading research on new heavy-ion nuclear reaction mechanisms.

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Neutron skin is an exotic phenomenon that occurs in unstable nuclei. In this study, the various effects of the neutron skin on nuclear reactions and their relationship with the properties of nuclear structures are reviewed. Based on numerous studies using theoretical models, strong correlations have been found between the neutron skin thickness and the neutron removal cross section, neutron/proton yield ratio, t/³He yield ratio, neutron–proton momentum difference, isoscaling parameter, photon production, reaction cross sections for neutron-induced reactions, charge-changing cross-sectional differences of mirror nuclei, astrophysical S-factor, and other quantities in nuclear reactions induced by neutron-rich nuclei. Moreover, the relationships between the neutron skin thickness and certain properties of the nuclear structure, such as α-cluster formation, α decay, nuclear surface, nuclear temperature, and proton radii difference of mirror nuclei, have also been investigated. Furthermore, it has also been shown that the neutron skin plays a crucial role in relativistic heavy-ion collisions. Experimentally, an unstable nucleus with a neutron skin can be generated by radioactive nuclear beam facilities, and the thickness of the neutron skin can be extracted by measuring the sensitive probes, which further helps impose stringent constraints on the equation of state of asymmetric nuclear matter and the properties of neutron stars.

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The exploration of reaction dynamics, particularly the breakup and fusion mechanisms of proton drip-line nuclei at energies around the Coulomb barrier, is crucial in the field of nuclear physics. This study reviews experimental investigations on the reactions induced by proton-rich nuclei, ⁷Be, ⁸B, and ¹⁷F, including elastic scattering and direct and fusion reactions at the near-barrier energies. In particular, we briefly introduce complete kinematic measurements of ⁸B+¹²⁰Sn and ¹⁷F+⁵⁸Ni at the energies of interest. Distinct reaction dynamics are observed for proton-rich nuclei compared with neutron-rich nuclei.

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A novel technique of isochronous mass spectrometry (IMS), termed Bρ-defined IMS, was developed at the experimental cooler-storage ring CSRe in Lanzhou for the first time. Two time-of-flight detectors were installed in a straight section of the CSRe, thereby enabling simultaneous measurements of the velocity and revolution time of each stored short-lived ion. This technique boosts the broadband precision, efficiency, sensitivity, and accuracy of mass measurements of short-lived exotic nuclides. Using Bρ-defined IMS, the masses of ²²Al, ⁶²Ge, ⁶⁴As, ⁶⁶Se, and ⁷⁰Kr were measured for the first time, and the masses of ⁶⁵As, ⁶⁷Se, and other 21 nuclides were redetermined with improved accuracy. Mass data have been used in studies of relevant issues regarding nuclear structures and nuclear astrophysics. Herein, we review the development of experimental techniques and main physical results and outline plans for future experiments.

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In the paper, we discuss the development of the multi-gap resistive plate chamber time-of-flight (TOF) technology and the production of the solenoidal tracker at RHIC (STAR) TOF detector in China at the beginning of the 21st century. Subsequently, recent experimental results from the first beam energy scan program (BES-I) at the Relativistic Heavy Ion Collider (RHIC) pertaining to measurements of collectivity, chirality, criticality, global polarization, strangeness, heavy-flavor, di-lepton and light nuclei productions are reviewed.

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Over the last decade, nuclear theory has made dramatic progress in few-body and ab initio many-body calculations. These great advances stem from chiral effective field theory (χEFT), which provides an efficient expansion and consistent treatment of nuclear forces as inputs of modern many-body calculations, among which the in-medium similarity renormalization group (IMSRG) and its variants play a vital role. On the other hand, significant efforts have been made to provide a unified description of the structure, decay, and reactions of the nuclei as open quantum systems. While a fully comprehensive and microscopic model has yet to be realized, substantial progress over recent decades has enhanced our understanding of open quantum systems around the dripline, which are often characterized by exotic structures and decay modes. To study these interesting phenomena, Gamow coupled-channel (GCC) method, in which the open quantum nature of few-body valence nucleons coupled to a deformed core, has been developed. This review focuses on the developments of the advanced IMSRG and GCC, and their applications to nuclear structure and reactions.

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Nucleus is essentially composed of protons and neutrons, which are commonly known as nucleons. Interestingly, some of nucleons may group together and exhibit collective behavior inside a nucleus. Such clustering effects have been known since the early stages of nuclear physics because of the observation and description of α-cluster decay from many heavy nuclei. Subsequent studies demonstrated that cluster structures exist in many nuclear systems, especially in weakly bound or excited states, and are complementary to the shell-like structures. In this review article, we provide a brief historical recall of the field, and follow it with a conceptual and logical description of the major theoretical models that have been frequently applied in the literature to describe nuclear clustering. Experimental methods and progress are outlined, recent outcomes are emphasized, and perspectives relevant to future studies of heavy neutron-rich systems are discussed.

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Nuclear astrophysics is a rapidly developing interdisciplinary field of research that has received extensive attention from the scientific community since the mid-twentieth century. Broadly, it uses the laws of extremely small atomic nuclei to explain the evolution of the universe. Owing to the complexity of nucleosynthesis processes and our limited understanding of nuclear physics in astrophysical environments, several critical astrophysical problems remain unsolved. To achieve a better understanding of astrophysics, it is necessary to measure the cross sections of key nuclear reactions with the precision required by astrophysical models. Direct measurement of nuclear reaction cross sections is an important method of investigating how nuclear reactions influence stellar evolution. Given the challenges involved in measuring the extremely low cross sections of nuclear reactions in the Gamow peak and preparing radioactive targets, indirect methods, such as the transfer reaction, coulomb dissociation, and surrogate ratio methods (SRM), have been developed over the past several decades. These are powerful tools in the investigation of, for example, neutron-capture (n,γ) reactions with short-lived radioactive isotopes. However, direct measurement is still preferable, such as in the case of reactions involving light and stable nuclei. As an essential part of stellar evolution, these low-energy stable nuclear reactions have been of particular interest in recent years. To overcome the difficulties in measurements near or deeply within the Gamow window, the combination of an underground laboratory and high-exposure accelerator/detector complex is currently the optimal solution. Therefore, underground experiments have emerged as a new and promising direction of research. In addition, to better simulate the stellar environment in the laboratory, research on nuclear physics under laser-driven plasma conditions has gradually become a frontier hotspot. In recent years, the CIAE team conducted a series of distinctive nuclear astrophysics studies, relying on the Jinping Underground Nuclear Astrophysics (JUNA) platform and accelerators in Earth’s surface laboratories, including the Beijing Radioactive Ion beam Facility (BRIF), as well as other scientific platforms at home and abroad. This research covered nuclear theories, numerical models, direct measurements, indirect measurements, and other novel approaches, achieving great interdisciplinary research results, with high-level academic publications and significant international impacts. This article reviews the above research and predicts future developments.

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The Large Hadron Collider (LHC), the world’s largest and most powerful particle accelerator, has been a pivotal tool in advancing our understanding of fundamental physics. By colliding heavy ions, such as lead ions, the LHC recreates conditions similar to those just after the Big Bang. This allows scientists to study the quark-gluon plasma (QGP), a state of matter in which quarks and gluons are not confined within protons and neutrons. These studies provide valuable insights into the strong force and the behavior of the early universe. In this paper, we present a comprehensive overview of recent significant findings from A Large Ion Collider Experiment (ALICE) at the LHC. The topics covered include measurements related to the properties of the QGP, particle production, flow and correlations, dileptons, quarkonia and electromagnetic probes, heavy flavor, and jets. Additionally, we introduce future plans for detector upgrades in the ALICE experiment.

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High-energy nuclear collisions encompass three key stages: the structure of the colliding nuclei, informed by low-energy nuclear physics, the initial condition, leading to the formation of quark-gluon plasma (QGP), and the hydrodynamic expansion and hadronization of the QGP, leading to final-state hadron distributions that are observed experimentally. Recent advances in both experimental and theoretical methods have ushered in a precision era of heavy-ion collisions, enabling an increasingly accurate understanding of these stages. However, most approaches involve simultaneously determining both QGP properties and initial conditions from a single collision system, creating complexity due to the coupled contributions of these stages to the final-state observables. To avoid this, we propose leveraging established knowledge of low-energy nuclear structures and hydrodynamic observables to independently constrain the QGP’s initial condition. By conducting comparative studies of collisions involving isobar-like nuclei – species with similar mass numbers but different ground-state geometries – we can disentangle the initial condition’s impacts from the QGP properties. This approach not only refines our understanding of the initial stages of the collisions but also turns high-energy nuclear experiments into a precision tool for imaging nuclear structures, offering insights that complement traditional low-energy approaches. Opportunities for carrying out such comparative experiments at the Large Hadron Collider (LHC) and other facilities could significantly advance both high-energy and low-energy nuclear physics. Additionally, this approach has implications for the future Electron-Ion Collider (EIC). While the possibilities are extensive, we focus on selected proposals that could benefit both the high-energy and low-energy nuclear physics communities. Originally prepared as input for the long-range plan of U.S. nuclear physics, this white paper reflects the status as of September 2022, with a brief update on developments since then.

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How does the strong force shape the structure of atomic nuclei? The STAR collaboration at the BNL Relativistic Heavy Ion Collider (RHIC) demonstrate that ultra-relativistic collision experiments give key insights into this fundamental question. From dedicated measurements in ²³⁸U+²³⁸U collisions at 100 GeV/nucleon energy, the STAR collaboration determine the deformed shape of the ²³⁸U nucleus, showing in particular that the experimental observables probe the elusive ground-state triaxiality of this isotope. These results pave the way to systematic characterizations of ground-state nuclear properties at high-energy colliders.

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