Oxygen collider Physicists working at CERN’s ATLAS experiment have gained insights into how cosmic rays interact with the atmosphere. (Courtesy: CERN/CC-BY-4.0)"> Oxygen collider Physicists working at CERN’s ATLAS experiment have gained insights into how cosmic rays interact with the atmosphere. (Courtesy: CERN/CC-BY-4.0)

Physicists at CERN have recreated the collisions that trigger cosmic-ray air showers in Earth’s atmosphere. Results from the ATLAS experiment on the Large Hadron Collider (LHC) show that none of the computer models used to simulate showers gets every detail right. Their measurements of particle production in proton–oxygen collisions are more than ten times more precise than the differences between the models – which could be improved by these latest results. This will be a step toward understanding the most energetic particles in the universe.

Cosmic rays are energetic particles (mostly protons) from outer space.…