| Abstract from DBPedia | The solar neutrino problem concerned a large discrepancy between the flux of solar neutrinos as predicted from the Sun's luminosity and as measured directly. The discrepancy was first observed in the mid-1960s and was resolved around 2002. The flux of neutrinos at Earth is several tens of billions per square centimetre per second, mostly from the Sun's core. They are nevertheless hard to detect, because they interact very weakly with matter, traversing the whole Earth as light does a thin layer of air. Of the three types (flavors) of neutrinos known in the Standard Model of particle physics, the Sun produces only electron neutrinos. When neutrino detectors became sensitive enough to measure the flow of electron neutrinos from the Sun, the number detected was much lower than predicted. In various experiments, the number deficit was between one half and two thirds. Particle physicists knew that a mechanism, discussed back in 1957 by Bruno Pontecorvo, could explain the deficit in electron neutrinos. However, they hesitated to accept it for various reasons, including the fact that it required a modification of the accepted Standard Model. They first pointed at the solar model for adjustment, which was ruled out. Today it is accepted that the neutrinos produced in the Sun are not massless particles as predicted by the Standard Model but rather mixed quantum states made up of defined-mass eigenstates in different (complex) proportions. That allows a neutrino produced as a pure electron neutrino to change during propagation into a mixture of electron, muon and tau neutrinos, with a reduced probability of being detected by a detector sensitive to only electron neutrinos. Several neutrino detectors aiming at different flavors, energies, and traveled distance contributed to our present knowledge of neutrinos. In 2002 and 2015, a total of four researchers related to some of these detectors were awarded the Nobel Prize in Physics.太陽ニュートリノ問題（たいようニュートリノもんだい、英: Solar neutrino problem）は、地球を貫通していくニュートリノの観測数が、太陽内部の理論的モデルから予測される値と一致しないとされていた問題である。1960年代半ばから問題とされてきたが、2002年に素粒子標準模型の修正を必要とするニュートリノ物理の新しい解釈であるニュートリノ振動の発見により解決された。ニュートリノ振動は伝搬の過程で各フレーバーのニュートリノの存在確率が周期的に変化（振動）する現象であり、ニュートリノが質量を持つことによって起きるとされている。太陽ニュートリノ問題の根本的な原因は、太陽内部で生成されるニュートリノがかつて用いられていた検出器では捉えられない別の2つのフレーバーのニュートリノに変化することであると説明することができる。 (Source: http://dbpedia.org/resource/Solar_neutrino_problem) |
