Scientists Simulate Cosmic Ray Showers in a Lab
Researchers at CERN have successfully recreated the initial moments of cosmic rainstorms by colliding oxygen atoms with protons, offering a new way to test how these high-energy particle showers form in Earth's atmosphere.
Every second, invisible particles zip through your body at nearly the speed of light. They originate from a storm high in the sky, where cosmic rays strike atoms in the atmosphere, breaking them apart into a shower that rains down to the ground. While scientists have studied these phenomena for over a century, a precise understanding of how these showers form has remained elusive. Now, a team of physicists has found a way to simulate this process in a controlled laboratory setting, removing the need to look to the sky for answers.
The study, published in Physical Review Letters, utilized CERN’s Large Hadron Collider in Switzerland to mimic the birth of these particle showers. By using the world’s first laboratory collisions of oxygen atoms with protons, researchers created a tangible environment to observe the early stages of cosmic rain. This approach allows for a level of precision that traditional atmospheric observation cannot match, providing a clearer window into the complex physics of interstellar matter.
Historical context of cosmic ray discovery
The story of cosmic rays begins in the early 20th century with physicist Victor Hess, who discovered them while ascending in hot air balloons. His instruments showed radiation levels rising unexpectedly with altitude, leading him to deduce that the source was space rather than the ground. This discovery earned him the 1936 Nobel Prize in Physics. Subsequent experiments revealed that this radiation contains exotic forms of matter, such as antimatter, muons, pions, and kaons, which were instrumental in building the modern theory of particle physics.
Today, we understand cosmic rays primarily as fast-moving atomic nuclei, mostly hydrogen. Evidence suggests they are ejected by extreme events in the universe, such as exploding stars and supermassive black holes. Beyond pure physics, these rays have practical applications. In the 1950s, they revolutionized archaeology through radiocarbon dating. More recently, geologists and archaeologists have used them to scan hidden chambers inside active volcanoes and reveal tombs within ancient Egyptian pyramids by measuring how rock deflects the flying particles.
Overcoming limitations of computer models
To decode the information carried by cosmic matter, scientists rely on computer simulations to model the particle rainstorm. However, a significant problem persists: different computer models often provide significantly varying predictions for how these showers form. To determine which model accurately describes reality, precise experimental data is essential. Until recently, no experiment had specifically focused on zooming into the birth of these particle showers, leaving a gap in our understanding that computer simulations alone could not fill.
For several years, researchers collaborated to make the case for reconfiguring existing instruments at CERN to address this gap. The trade-off for this precision is the complexity of the setup, requiring a shift from standard collider operations to a specialized configuration. This effort culminated in July 2025, when scientists pioneered the experiment by colliding oxygen atoms with protons for the first time, specifically designed to mimic the interaction of cosmic rays with the atmosphere.
Experimental setup and precise results
In this experiment, a proton beam acted as the cosmic ray, while an oxygen beam played the role of Earth’s atmosphere. The energy from each collision converted into a spray of particles, effectively recreating the first moments of a cosmic rainstorm in a controlled environment. The team used the ATLAS experiment, a giant detector the size of a football field, to analyze the events. High-speed silicon sensors captured images of the particle sprays, allowing for detailed analysis of the interaction.
The results, as reported by GN technics/space, were striking. The team measured both the number of particles created and their outgoing energy levels with a precision more than ten times greater than previous computer model predictions. These measurements will help pinpoint the composition of high-energy cosmic rays, distinguishing between hydrogen and heavier atoms. This offers key clues about their origins and strengthens the link between particle physics and astrophysics, providing a more robust framework for understanding the universe's most energetic events.
