Collaborative Research: Solar Neutrino Science with Borexino: The Quest for CNO Neutrinos

太阳中微子研究已经发现了大量的中微子和味道混合，并且正在进入一个精确测量可以为太阳的结构和组成提供独特探测的时代。碳-氮-氧（CNO）循环是恒星将氢转化为氦并释放电子-中微子的聚变反应之一。CNO的中微子通量取决于太阳核心的碳丰度。对CNO通量的测量将是对太阳核心金属丰度（氢或氦以外元素的丰度）的第一次直接测量。它可以测试太阳均匀性的基本假设，并提供关于太阳内部不透明的关键信息，这对日震学很重要。因此，这样的研究可能会对我们对太阳、恒星天体物理学、行星和恒星形成之间的联系以及基本的中微子物理学的理解产生重大影响。Borexino是位于意大利格兰萨索国家实验室的液体闪烁体探测器，对太阳中微子具有独特的灵敏度。Borexino研究项目涉及许多本科生和研究生。指导和培训合作机构和其他学校的年轻研究人员一直是重中之重。这三个小组将继续让本科生参与这项研究，并将研究成果传播给更广泛的社区。这里资助的研究计划测量12-C和15-N的催化反应产生的中微子，这些反应将4个质子转化为4-He，从13-N和15-O的衰变中产生中微子。CN中微子通量直接取决于太阳核心中12-C和15-N的丰度，它们的测量将是太阳核心中金属丰度（比4-He重的元素）的第一次直接测量。这一结果将影响深远，因为太阳的组成是天体物理学中许多重要课题的基础，包括恒星结构、恒星演化和恒星大气，等等。此外，它还将解决“太阳成分问题”，即最近太阳光球光谱分析的进展（倾向于低金属丰度）和日震学的进展（倾向于高金属丰度）所确定的金属丰度的明显分歧。由于对标准太阳模型的修改来解释不均匀的太阳成分并不是很成功，“太阳成分问题”仍然是标准太阳模型中一个无法解释的缺陷。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。

Solar neutrino research has already discovered massive neutrinos and flavor mixing and is moving into an era where precision measurements can provide a unique probe of the structure and composition of the Sun. The carbon-nitrogen-oxygen (CNO) cycle is one of the fusion reactions by which stars convert hydrogen to helium, releasing electron-neutrinos. The CNO neutrino flux depends on the abundance of carbon in the core of the Sun. A measurement of the CNO flux would be the first direct measurement of the solar metallicity (the abundance of elements other than hydrogen or helium) in the core of the Sun. It could test the fundamental assumption of homogeneity in the Sun and provide crucial information regarding opacities in the solar interior that are important for helioseismology. Such studies could thus have a great impact on our understanding of the Sun, stellar astrophysics, the link between planetary and stellar formation, as well as basic neutrino physics. Borexino is a liquid scintillator detector, located at the Gran Sasso National Laboratory in Italy, with a unique sensitivity to solar neutrinos.The Borexino research program has involved many undergraduate and graduate students. Mentoring and training young researchers at the collaborating institutions and other schools has always been a high priority. The three groups will continue to involve undergraduate students in this research and disseminate research to the broader community.The research funded here plans to measure neutrinos from the catalytic reactions on 12-C and 15-N which convert four protons to 4-He, producing neutrinos from the beta decays of 13-N and 15-O. The CN neutrino flux depends directly on the abundance of 12-C and 15-N in the core of the Sun, and their measurement would be the first direct measurement of the metallicity (elements heavier than 4-He), in the core of the Sun. This result will be far reaching because the solar composition is the basis for many important topics in astrophysics, including stellar structure, stellar evolution, and stellar atmospheres, to name a few. In addition, it will address the 'solar composition problem', the apparent disagreement in metallicity determined from recent advances in analysis of solar photospheric optical spectra, which favors a low metallicity, and advances in helioseismology, which favors high metallicity. Since modifications of the Standard Solar Model to explain a non-uniform solar composition have not been very successful, the 'solar composition problem' remains an unexplained flaw in the Standard Solar Model.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.