Newswise — Another long-standing mystery in particle physics has finally been solved. An international research team of the ALICE experiment at CERN’s particle accelerator, led by researchers from the Technical University of Munich (TUM), has for the first time directly observed how light atomic nuclei and their antiparticles – so-called deuterons and antideuterons – are formed in extremely high-energy particle collisions.
The result: The protons and neutrons necessary for the formation of deuterons are released during the decay of very short-lived, highly energetic particle states (so-called resonances) and then bind together. The same holds true for their antimatter counterparts. The findings were published in the renowned journal Nature.
In proton collisions at the Large Hadron Collider (LHC) at CERN, temperatures arise that are more than 100,000 times hotter than the center of the Sun. Until now, it had been entirely unclear how fragile particles such as deuterons and antideuterons could survive under these conditions. In such an environment, light atomic nuclei like the deuteron – consisting of just one proton and one neutron – should in fact disintegrate immediately, since the binding force that holds them together is comparatively weak. Yet such nuclei had repeatedly been observed. It is now clear: about 90 percent of the observed (anti)deuterons are produced through this mechanism.
Better understanding of the universe
TUM particle physicist Prof. Laura Fabbietti, a researcher in the ORIGINS Cluster of Excellence and SFB1258, emphasizes: “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, explains: “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.”
