CERN recreates the birth of cosmic particle showers

Physicists at CERN have recreated the first moments of cosmic particle showers in the laboratory, providing new evidence to test how scientists interpret the particles arriving from space.

Cosmic rays are fast-moving atomic nuclei. When they strike atoms high in Earth’s atmosphere, they trigger showers of other particles. Researchers use computer simulations to work backwards from these showers and learn about the original cosmic ray, but different models give different answers.

To put those models to the test, an international team used the Large Hadron Collider to collide proton beams with oxygen beams for the first time in July 2025. The protons stood in for incoming cosmic rays, while the oxygen represented a component of the atmosphere.

The ATLAS detector recorded the resulting sprays of particles. By measuring their numbers, energies and directions, the team produced detailed portraits of how a shower begins. The findings, published in Physical Review Letters, showed that existing models did not accurately describe these interactions.

The new data should help researchers distinguish cosmic rays made of hydrogen from those made of heavier elements. That could offer clues to their origins and help scientists investigate some of the universe’s most extreme environments.