Window on the Universe: Equation of State of Asymmetric Nuclear Matter

由LIGO-Virgo合作进行的GW170817引力波（GW）对中子星（NS）合并的壮观观测伴随着伽马射线、光学和无线电信号的探测。这些协调观测是美国尖端科学投资的成果。这些投资开创了同步多信使天体物理学的新时代，并提供了NS合并、千新星和伽马射线爆发之间的明确联系，以及NS合并和重元素核合成之间的明确联系。拟议的研究计划扩大了这些多信使研究，包括来自支持NS的富中子物质中力的实验约束的相关信息。它通过关注依赖于中子质子不平衡的核力的性质，解决了2015年核科学长期计划中关于中子星和稀密核物质性质的问题。密歇根州立大学（Michigan State University）和美国物理研究所（FRIB）赞助针对代表性不足的物理学学生的研究，这将有助于吸引不同群体的有才华的本科生、研究生和博士后参与该项目。这些年轻的科学家将学习探测器的设计和建造、复杂的多参数数据分析、探测器模拟和理论建模、机器学习和贝叶斯推理分析。这种培训为他们在核科学以及对技术进步和国家安全重要的其他关键领域的未来工作中发挥领导作用做好准备。GW170817引力波观测和中子星内部成分探测器（NICER）最近关于中子星半径的信息都限制了中子星内总压力和物质密度之间的关系。然而，这两个天文观测都没有孤立对称能。对称能是状态方程（EoS）中的一个术语，它是由物质中中子和质子数量的不平衡引起的。它对NS的稳定性起着主导作用。对称能决定了中子和质子的相对数量，以及液态核结束和固体地壳开始处的密度和压力。对称能还决定着中子星内是否存在反物质或奇异物质。该小组将通过实验研究来研究对称能，并通过改变中子和质子的相对数量以及系统密度从正常核物质密度的四分之一到两倍来分离对称能的作用。他们将在日本理化研究所进行实验，使用最先进的仪器和理论与实验之间的合作努力，将这些发现与多信使天文学的新兴结果联系起来。通过将这些对称能的新测量结果与现有的对含有等量中子和质子的对称物质的实验约束相结合，他们还将获得同样具有根本意义的纯中子物质的极限。虽然学生培训的重点是科学技术进步，但他们也将让年轻科学家参与外联活动，使这门科学更容易为非科学家所接受。他们创建了一些网站，利用虚拟现实应用程序来说明核碰撞、宇宙射线的探测以及我们的时间投影室的工作原理。通过这样的努力，他们将努力使科学对公众更具吸引力和令人兴奋。该项目推进了“宇宙之窗：多信使天体物理学时代”的目标，这是美国国家科学基金会未来投资的十大理念之一。该奖项反映了美国国家科学基金会的法定使命，并通过使用基金会的知识价值和更广泛的影响审查标准进行评估，被认为值得支持。

Windows on the Universe: Equation of state of Asymmetric Nuclear Matter The spectacular GW170817 gravitational wave (GW) observations of a Neutron Star (NS) merger by the LIGO-Virgo collaboration were accompanied by the detection of gamma-rays, optical and radio signals. These coordinated observations were the fruit of cutting-edge scientific investments by the U.S. These investments usher in a new era of synchronous multi-messenger astrophysics, and provide definitive links between NS mergers, kilonovae and gamma-ray bursts, and between NS mergers and the nucleosynthesis of heavy elements. The proposed research plan broadens these multi-messenger studies to include relevant messages from experimental constraints on the forces within neutron-rich matter that support the NS. It addresses questions of the 2015 Long Range Plan for Nuclear Science concerning the nature of neutron stars and dilute and dense nuclear matter by focusing on properties of nuclear forces that depend on neutron-to-proton imbalance. Michigan State University and FRIB sponsor research for under-represented physics students, which will help to attract a diverse group of talented undergraduate students, graduate students and postdocs to this project. These young scientists will learn about detector design and construction, complex multi-parameter data analyses, detector simulations and theoretical modeling, machine learning and Bayesian inference analyses. This training prepares them for leadership roles in the future work force both in nuclear science but also in other key areas important for technological advancement and national security. Both the GW170817 gravitational wave observations and recent messages on Neutron Star (NS) radii from the Neutron star Interior Composition Explorer (NICER) constrain the relationship between the total pressure and the matter density within NS. Neither astronomical observation isolates the symmetry energy, however. The symmetry energy is a term in the Equation of State (EoS) that arises from the imbalance in the numbers of neutrons and protons in the matter. It plays a dominant role regarding the stability of a NS. The symmetry energy governs the relative numbers of neutrons and protons, and the density and pressure where the liquid NS core ends and solid crust begins. The symmetry energy also governs whether anti matter or strange matter exist within neutron stars. The group will study the symmetry energy via experimental studies and isolate its role by varying the relative numbers of neutrons and protons and also the density of the system from ¼ to twice normal nuclear matter density. They will perform experiments at RIKEN in Japan, using cutting edge instrumentation and a collaborative effort between theory and experiment to connect the findings to emerging results from multi-messenger astronomy. By combining these new measurements of the symmetry energy with existing experimental constraints on the EoS of symmetric matter which contains equal numbers of neutrons and protons, they will also obtain the EoS of pure neutron matter which is also of fundamental interest. While the focus of the student training is on scientific and technological advancement, they will also engage young scientists in outreach activities to make this science more accessible to non-scientists. They have created websites using virtual reality apps to illustrate nuclear collisions, the detection of cosmic rays and the working principles of our time projection chamber. By such efforts, they will endeavor to make the science more appealing and exciting to the general public.This project advances the objectives of "Windows on the Universe: the Era of Multi-Messenger Astrophysics", one of the 10 Big Ideas for Future NSF Investments.This award reflects NSF's statutory mission and has been deemed worthy of support through evaluation using the Foundation's intellectual merit and broader impacts review criteria.