Seeking ghost particles high and low

摘要

Massive particle detectors in Italy and the South Pole are closing in on ghostly visitors from deep beneath Earth's crust and far out in space. These barely there particles, called neutrinos, are nearly massless, neutrally charged and produced during radioactive decay. They rarely interact with other particles - trillions pass through your body every second. That hasn't stopped physicists trying to spot them. The Borexino detector in Gran Sasso, Italy - a giant metal sphere full of liquid scintillator that flashes when a neutrino interacts with it - has just confirmed the existence of neutrinos coming from Earth's crust and mantle. Such particles had been seen before, but only faintly. Borexino now has 2056 days of data and the team says there is about a 1 in 275 million chance that if s wrong (Physical Review D, doi.org/6pf).