Ultra High Energy Cosmic Rays

The origin of ultra-high-energy cosmic rays is a question that makes it onto many top-unsolved-problems-in-physics lists.

The math says that these particles, which carry in excess of 1019 electron volts, or eV,  from somewhere in outer space, are far too energetic not to have interacted themselves out of existence before reaching the earth. And yet every year scientists see evidence in the earth’s atmosphere of a handful of these particles, which have several million times the energy of the protons being collided at the Large Hadron Collider.

The TAUWER experiment looks at particle showers that originate from tau neutrinos that take short paths through the earth (inset). An ideal site to observe these events is a mountain bowl. Image courtesy of Maurizio Iori.

 

Cosmic rays with these amazing energies are an existence proof that the LHC won’t trigger unusually dangerous physics at energies it can reach. The big question is how these particles obtain their energy, and what keeps them intact till they reach Earth.

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