Particle showers caused by natural ultra-high-energy collisions in Earth's atmosphere produce more muons — heavier cousins of the electron — than current physics models can explain.
Using the Pierre Auger Observatory in Argentina, Glennys Farrar of New York University and her colleagues studied showers of particles produced when 411 ultra-high-energy cosmic rays — atomic nuclei thought to originate outside the Galaxy — collided with air molecules. They also studied the fluorescent light the cascades created. The team found that the collisions, which are 10 times more energetic than those generated at the Large Hadron Collider (LHC) near Geneva in Switzerland, produced 30–60% more muons than simulations based on LHC results predict.
The results suggest that either the underlying models contain flaws, or that physics is fundamentally different at these higher energies.