Wednesday, November 29, 2017

Cosmic Neutrinos Can be Absorbed by Planet Earth

Image Credit: Martin Wolf/IceCube/NSF
 Scientists using the IceCube Observatory located near the South Pole have discovered that neutrinos can be absorbed by our Planet Earth. With almost no mass and no charge, these particles rarely interact with matter. Yet tens of trillions of neutrinos pass through our bodies every second.
 Previous theories predicted that at high energies, neutrinos can be expected to interact with matter and be absorbed by the Earth instead of passing through the planet.
 “We knew that lower-energy neutrinos pass through just about anything, but although we had expected higher-energy neutrinos to be different, no previous experiments had been able to demonstrate convincingly that higher-energy neutrinos could be stopped by anything,” said Penn State Professor Doug Cowen. “However, the neutrino does have a tiny probability to interact, and this probability increases with energy. That probability is what scientists call the neutrino cross section.”
 The new measurements recorded by IceCube determined the neutrino cross section energies to be about 6.3 TeV and 980 TeV, energy levels significantly higher than previously measured.
“We looked mostly at neutrinos created when high-energy cosmic rays crash into the nuclei of nitrogen or oxygen in the Earth’s atmosphere. Those collisions produce a cascade of subatomic particles that can generate neutrinos,” the team of physicists said.
“The sample also included a smaller number of neutrinos probably created in yet-to-be identified cosmic accelerators such as black holes.”
“We found that fewer of the most energetic neutrinos were making it to the detector from the northern hemisphere, where the particles would have to transit the entire Earth, including the dense core of our planet, before reaching the IceCube sensors. From less obstructed, near horizontal trajectories, more neutrinos were detected.”
 In the end, these neutrino observations conformed to the Standard Model of Physics, leading to some disappointment amongst the team members.

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