ALICE Experiment Pinpoints Light Nuclei Formation via Resonance Decay at CERN

Scientists with the A Large Ion Collider Experiment (ALICE) at CERN's Large Hadron Collider (LHC) have established the dominant mechanism for the creation of light atomic nuclei, such as deuterons and antideuterons, within high-energy particle collisions. This finding, published in the journal Nature on December 10, 2025, resolves a long-standing question in nuclear physics regarding how these fragile structures survive temperatures exceeding one hundred thousand times that of the Sun's core.

The research, led by investigators from the Technical University of Munich (TUM), analyzed data from high-energy proton collisions recorded during the LHC's second run to determine the primary formation pathway. The core discovery indicates that the necessary protons and neutrons for these nuclei do not exist instantaneously at the moment of collision. Instead, the investigation demonstrates that these constituents arise from the sequential decay of short-lived, high-energy particle states known as resonances, specifically citing the $\Delta(1232)$ resonance as the source.

Measurements from the ALICE detector, which tracks particles from these violent events, show that approximately 90 percent of the observed (anti)deuterons form through this specific resonance-decay pathway. This process occurs as the collision system expands and cools, allowing newly generated protons or neutrons to combine through final-state nuclear fusion in a comparatively less energetic environment. Professor Laura Fabbietti of TUM stated that the experimental evidence confirms light nuclei coalesce when conditions are "somewhat cooler and calmer," rather than during the initial, intensely hot phase of the interaction.

This work represents a significant advancement in comprehending the strong interaction, the fundamental force binding atomic nuclei, by recreating conditions akin to the universe's nascent moments. Dr. Maximilian Mahlein noted the broader consequences, highlighting the relevance to astrophysics in refining the interpretation of cosmic ray data. Improved theoretical models based on this new understanding of light nuclei production may offer avenues for investigating the nature of dark matter, a central focus of the ORIGINS Cluster of Excellence, which merges particle physics, astrophysics, and biophysics.

Further recognition for the collaborative efforts at CERN arrived in April 2025, when Professor Laura Fabbietti and Professor Lukas Heinrich were jointly awarded the 2025 Breakthrough Prize in Fundamental Physics on April 5. This prize was distributed among 13,508 researchers involved in the LHC collaborations (ALICE, ATLAS, CMS, and LHCb) for high-precision testing of the Standard Model. Prof. Fabbietti, a coordinator within the ORIGINS Cluster, noted that her participation at CERN was a "decisive turning point" in her career due to the data quality, while Prof. Heinrich's group at TUM is also involved in the ATLAS project. The ALICE experiment's precise comparison of light nuclei and antinuclei properties underscores the diversity of research conducted at the facility.