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，并正在进入一个精确测量可以提供一个独特的探测器太阳的结构和组成的时代。碳-氮-氧(CNO)循环是恒星将氢转化为氦，释放电子中微子的聚变反应之一。CNO中微子的流量取决于太阳核心中碳的丰度。对CNO通量的测量将是第一次直接测量太阳核心中的太阳金属丰度(氢或氦以外的元素的丰度)。它可以检验太阳同质性的基本假设，并提供有关太阳内部不透明的关键信息，这些信息对日震学很重要。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的理解产生重大影响。Borexino是一种液体闪烁体探测器，位于意大利Gran Sasso国家实验室，对太阳中微子具有独特的敏感性。Borexino研究项目涉及许多本科生和研究生。在合作机构和其他学校指导和培训年轻研究人员一直是一个高度优先的问题。这三个小组将继续让本科生参与这项研究，并向更广泛的社区传播研究。这里资助的研究计划测量12-C和15-N上催化反应产生的中微子，这些反应将四个质子转化为4-He，从13-N和15-O的β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，它们的测量将是第一次直接测量太阳核心中的金属丰度(重于4-He的元素)。这一结果将是深远的，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，仅举几例。此外，它还将解决“太阳组成问题”，即从太阳光球光谱分析的最新进展中确定的金属丰度的明显不一致，这有利于低金属丰度，以及在日震学方面的进展，它有利于高金属丰度。由于对标准太阳模型的修改以解释不均匀的太阳组成并不是非常成功，标准太阳模型中的一个无法解释的缺陷仍然存在。这项裁决反映了NSF的法定使命，并通过使用基金会的智力优势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.