THIS is the story of a particle that has refused to die. For 50 years, it has haunted particle physics, with hints of its presence appearing in maddeningly ambiguous ways. Some believe they have seen it. Others think it is a figment of our imagination. But every time we think it is definitely not there, a sudden gust of wind knocks over the furniture and once more there is room for doubt.
Elusive though it is, the sterile neutrino would be a real boon. It could make sense of experimental anomalies stretching back decades, and give us the first confirmed glimpse of physics beyond what we know. It could even explain the strangely low masses of the ordinary neutrinos, as well as offering a convincing candidate for dark matter.
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