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Muon surplus leaves physicists searching for answers

Excess of subatomic particles produced by cosmic rays might signal new state of matter

9:00am, November 4, 2016
Pierre Auger Observatory

MANY MUONS Scientists at the Pierre Auger Observatory use telescopes (pictured above) and water tanks to detect showers of particles created by high-energy protons or atomic nuclei from space. Scientists have found more muons, or larger versions of electrons, than expected in such showers.

Muons, electrons’ heftier cousins, rain down through the Earth’s atmosphere in numbers higher than physicists expect. The discrepancy could simply point to a gap in physicists’ understanding of the nitty-gritty physics of particle interactions, or perhaps something unexpected is going on, such as the creation of a new state of matter.

When cosmic rays — spacefaring protons or atomic nuclei — smash into the atmosphere at ultrahigh energies, they launch a cascade of many other types of particles, including muons. New observations made at the Pierre Auger Observatory detect about 30 percent more muons than simulations predict, scientists report October 31 in Physical Review Letters.

The Auger observatory, located in Argentina, uses telescopes to observe faint light from particle showers in the atmosphere, and detects particles that reach the ground using

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