Travel grant to support measurement of the astrophysical 4He(3He,g)7Be rate at TRIUMF

来自太阳的能量对维持地球上的生命至关重要，它是一系列核反应的结果，这些反应将氢转化为氦，释放出核结合能。这些反应中的几个还会产生中微子，这种相互作用非常弱的粒子可以从太阳逃逸到地球上。在地面探测器中对这些中微子的测量导致了范式的转变，因为它揭示了中微子有质量(以前我们认为它们是无质量的)。实验工作现在的目标是准确测量中微子的能谱，从中可以确定关于中微子结构的重要细节。然而，矛盾的是，极限并不是测量的准确性，而是太阳产生的中微子通量的不确定性。这种不确定性的产生是因为，由于反应截面中的不确定性，我们无法正确地模拟核反应序列。其中一个关键反应是3He和4He核聚变形成7Be，而反应速率的不确定性是确定高能中微子通量的主要不确定性。去年报道的测量结果显示，反应速度比之前认为的要高，这让情况变得更加混乱。最近，人们对这一反应产生了进一步的兴趣，因为与基于大爆炸核合成模型的预测相比，在非常古老的恒星中观察到的锂元素的数量(因此代表大爆炸中产生的元素)存在严重差异。这种差异的起源可能是恒星演化的某个未知方面，但目前的反应速度不确定正在损害解开这一点的努力。这项测量是一系列实验的一部分，采用互补方法，我们设计了解决这种差异和减少横截面测量中的实验不确定度。

The energy from our Sun, which is essential to maintain life here on Earth, results from a sequence of nuclear reactions which turn Hydrogen into Helium, releasing nuclear binding energy. Several of these reactions also result in the production of neutrinos, very weakly interacting particles which can escape from the Sun and reach us here on Earth. The measurement of these neutrinos in Earth based detectors has resulted in a paradigm shift, since it has revealed that neutrinos have a mass (previously we thought they were massless). The experimental effort is now directed at accurate measurements of the energy spectrum of the neutrinos, from which important details about the structure of neutrinos can be determined. However, paradoxically it is not the accuracy of the measurements which is the limit, but the uncertainty on the flux of neutrinos generated in the Sun. This uncertainty arises because we cannot model the nuclear reaction sequence properly because of uncertainties in the reaction cross sections. One of the key reactions is the fusion of a 3He and a 4He nucleus to form 7Be and the uncertainty in this reaction rate is the remaining major uncertainty in determining the high energy neutrino flux. The situation has been further confused by measurement reported last year which shows a higher reaction rate than previously believed. Further recent interest in this reaction has arisen because of a serious discrepancy in the amount of the element lithium which is observed in very ancient starts (and so which represents that produced in the Big Bang) compared with what is predicted based on models of Big Bang nucleosynthesis. The origin of the discrepancy is probably in some unknown aspect of the stellar evolution, but the present reaction rate uncertainties are compromising efforts to unravel this. This measurement is part of a sequence of experiments, using complementary approached, we have designed to resolve this discrepancy and to reduce the experimental uncertainty in the cross section measurement.