Large Hadron Collider finally explains how fragile matter forms
In collisions at CERN’s Large Hadron Collider, hotter than the Sun’s core by a staggering margin, scientists have finally solved a long-standing mystery: how delicate particles like deuterons and their antimatter twins can exist at all. Instead of forming in the initial chaos, these fragile nuclei are born later, when the fireball cools, from the decay of ultra-short-lived, high-energy particles.
Scientists have now clarified how deuterons form under extreme conditions. Protons and neutrons needed to create these tiny nuclei are released when extremely short-lived, high-energy particle states decay (so-called resonances). Once freed, the particles can join together to form deuterons. The same process also explains how antideuterons, made of antimatter, are produced. These results were reported in the journal Nature.
At CERN's Large Hadron Collider (LHC), proton collisions generate temperatures more than 100,000 times hotter than the Sun's core. For years, researchers did not understand how delicate particles like deuterons and antideuterons could exist in such intense heat. A deuteron contains just one proton and one neutron, held together by a relatively weak force. Under these conditions, such a light atomic nucleus should break apart almost instantly. Even so, experiments kept detecting them. Researchers have now shown that roughly 90 percent of the observed (anti)deuterons form through this newly identified process, rather than surviving the initial blast.
New Insight Into the Strong Interaction
TUM particle physicist Prof. Laura Fabbietti, a member of the ORIGINS Cluster of Excellence and SFB1258, highlights the importance of the discovery. "Our result is an important step toward a better understanding of the 'strong interaction' -- that fundamental force that binds protons and neutrons together in the atomic nucleus. The measurements clearly show: light nuclei do not form in the hot initial stage of the collision, but later, when the conditions have become somewhat cooler and calmer."
Dr. Maximilian Mahlein, a researcher at Fabbietti's Chair for Dense and Strange Hadronic Matter at the TUM School of Natural Sciences, adds that the findings have broader implications. "Our discovery is significant not only for fundamental nuclear physics research. Light atomic nuclei also form in the cosmos -- for example in interactions of cosmic rays. They could even provide clues about the still-mysterious dark matter. With our new findings, models of how these particles are formed can be improved and cosmic data interpreted more reliably."
CERN and the Large Hadron Collider
CERN (Conseil Européen pour la Recherche Nucléaire) is the world's largest center for particle physics research. Located near Geneva on the border between Switzerland and France, it is home to the LHC, a 27-kilometer-long underground ring accelerator. Inside the LHC, protons are smashed together at nearly the speed of light. These collisions recreate conditions similar to those shortly after the Big Bang, reaching temperatures and energies not found anywhere else today. This allows scientists to study matter at its most basic level and test the fundamental laws of nature.
ALICE and the Birth of Matter
One of the LHC's key experiments is ALICE (A Large Ion Collider Experiment), which focuses on understanding the strong interaction that holds atomic nuclei together. ALICE functions like an enormous camera, able to track and reconstruct up to 2000 particles produced in a single collision. By doing so, researchers aim to recreate the universe's earliest moments and learn how a hot mixture of quarks and gluons eventually formed stable atomic nuclei and, ultimately, all matter.