Science has found clues that could help solve one of the most fundamental mysteries of the universe.

For decades, scientists have been trying to understand why matter dominates antimatter in the universe. A key concept in this quest is CP violation – a phenomenon that describes the differences in behavior between particles and their antiparticles.

 

A CP violation occurs when a particle and its corresponding antiparticle do not exhibit identical behavior under charge (C) and spatial symmetry (P) transformations. In fact, some decay processes occur more frequently than their 'CP counterparts', due to the interference between the phases of the weak and strong interactions. This asymmetry is considered a key factor in explaining the imbalance between matter and antimatter in the universe.

Previous studies have found surprisingly large CP violation effects during the decay of charm quark-containing mesons. However, the results for charm quark-containing baryons have not been very clear. To fill this gap, Professor Xiao-Gang He and Dr. Chia-Wei Liu of the Tsung-Dao Lee Institute (TDLI), Shanghai Jiao Tong University, conducted a systematic analysis. By combining SU(3) flavor symmetry theory with the final-state rescattering model, the research team predicted a significantly stronger CP violation effect in charm baryon decay than previous estimates.

A baryon is a subatomic particle consisting of three quarks bound together by the strong nuclear force, with a baryon number of +1, thus distinguishing it from a meson. Protons (uud) and neutrons (udd) are the lightest baryons, making up the atomic nucleus. There are also heavier baryons containing strange quarks, charm quarks, or bottom quarks, and these often decay into lighter baryons.

 

The study particularly highlights the role of final-state rescattering in CP violations. This process allows particles to continue interacting with each other after initial decay, thereby creating strong phases – a necessary condition for CP violations to occur. According to the team's results, the degree of matter-antimatter asymmetry in baryon charm decay can reach one-thousandth, much higher than previously predicted theoretically.

Founded in 2017, TDLI focuses on fundamental physics research. Professor He, head of the Department of Particle and Nuclear Physics, said: "Research on CP violations in charm particles opens new avenues for experimentation and provides deeper insights into the underlying mechanisms of the universe's matter-antimatter asymmetry. It also creates a crucial opportunity to test the Standard Model and explore new forms of physics."

The Standard Model is a theory that describes how the fundamental components of matter interact with each other, governed by four fundamental forces: gravity, electromagnetism, the strong nuclear force, and the weak nuclear force.

Currently, these predictions are still awaiting experimental verification. Facilities such as BESIII in China, LHCb at CERN, and Belle II in Japan have shown some capability in detecting CP violations in charm decay processes. In the future, the Super Tau-Charm Facility (STCF) that China is planning to build is expected to offer even higher sensitivity, allowing for even more accurate measurements.

This research marks a step forward in answering one of physics' most fundamental questions: why is there more matter than antimatter? By demonstrating a larger CP violation effect in the baryon charm, the work opens new avenues of experimental research and may provide clues about physics beyond the Standard Model.