Earth absorbs 'ghost particles' that carry high energy

Some high-energy neutrinos are absorbed when passing through the Earth.

IceCube includes many optical sensors wrapped in very clean Antarctic ice.(Photo: Jamie Yang.)

Neutrinos are known as "" because they are capable of passing solid objects easily. However, the international team working at IceCube (the world's largest neutrino detector in Antarctica) found that some of these subatomic particles were stopped when their pathway encountered our planet. . The results of the study are published in the November 22 issue of the journal Nature.

Neutrino particles interact very weakly with matter. A neutrino can move a light-year path (10 trillion km) in lead metal without colliding with any atom. The neutrino particles recorded by IceCube detectors carry very high energy. This is an important factor, because neutrinos with higher energy are more likely to interact with matter and will be absorbed by the Earth.

The structure of the IceCube includes an array of 5,160 optical sensors - Digital Optical Module (DOMs) - the size of a basketball. They are enclosed in 1 km3 of very clean Antarctic ice, near the South pole of the Earth. Sensors do not directly observe neutrinos but measure blue light, or Cherenkov radiation, emanating from some other particles such as muons - products created when neutrinos interact with ice.

By measuring Cherenkov radiation in the area inside or near the detector, IceCube can evaluate and estimate the direction and energy of neutrino particles. The team found that the number of neutrinos carrying high energy passing through the Earth to the IceCube detector was less than the number of neutrinos coming from the path less obstructed, for example particles moving close to horizontal.

The moving path of neutrinos to the IceCube detector.(Photo: Nature.)

Most neutrinos recorded by the IceCube detector in this study have millions of times more energy than the familiar neutrinos produced by sources like the Sun or nuclear power plants. They form in the Earth's atmosphere through a process derived from cosmic rays or unknown sources outside the Earth's atmosphere.

"Understanding how neutrinos interact is the key to IceCube's work," said Francis Halzen, a professor of physics at the University of Wisconsin-Madison (USA) working on the IceCube project.