In the early moments following the Big Bang, matter and antimatter should have been created in equal amounts. However, 13.8 billion years later, the Universe is overwhelmingly made of matter, with antimatter nearly absent. This strange imbalance has baffled scientists for decades, hinting that something must have occurred to tilt the balance in favor of matter.
One of the leading theories to explain this disparity is charge–parity (CP) violation, a phenomenon predicted by the Standard Model of particle physics. CP violation refers to a small but measurable difference in how matter and antimatter behave.
However, the Standard Model predicts that the number of CP violations is far too small to account for the vast predominance of matter. So far, CP violation has only been observed in certain particle decays, notably in mesons — particles made of quarks and an antiquark. To truly understand the origins of the matter-antimatter imbalance, scientists need to see CP violation in a broader range of particles, particularly baryons, composed of three quarks.
Now, new findings from the LHCb collaboration at CERN‘s Large Hadron Collider (LHC) have provided significant new evidence of CP violation in two key areas of particle physics: the decays of baryons and the decays of beauty hadrons into charmonium particles. These results could offer important clues about the matter-antimatter puzzle.
The long-Standing mystery of matter and antimatter solved
First Study: Evidence in Bottom Lambda Baryon Decays
In their first study, the LHCb team analyzed proton-proton collision data collected during the LHC’s first and second runs. They focused on the decays of the bottom lambda baryon (Λ_b), specifically its decay into a lambda baryon and two kaons. By comparing the decays of the bottom lambda baryon and its antimatter counterpart, the team looked for any differences that would signal CP violation.
The results were striking: a difference was observed between the number of decays of the bottom lambda baryon and its antimatter partner, with a statistical significance of 3.2 standard deviations. This marks the first evidence of CP violation in this particular decay process. While not definitive proof, this finding brings scientists closer to understanding how CP violation might occur in baryons, helping to explain why the Universe is made mostly of matter.
The universe is nearly 10 percent more homogeneous than expected
Second Study: CP Violation in Beauty Meson Decays
In their second study, the LHCb team turned their attention to beauty mesons — particles made up of a bottom quark and an antiquark. They focused on the decay of a charged beauty meson into a J/psi particle and a charged pion. The J/psi is a charmonium particle consisting of a charm quark and a charm antiquark.
Using a similar analysis to the one applied to the bottom lambda baryon, the researchers again compared the beauty meson’s decays and its antimatter counterpart. The results revealed a significant difference in the decays, with a CP violation signal reaching a 3.2 standard deviation significance.
A Step Closer to Solving the Puzzle
The findings from these two studies represent key steps forward in the search for CP violation in baryons and hadrons, shedding new light on the fundamental question of why the Universe is made almost entirely of matter. However, scientists caution that further data is needed to confirm these results and establish whether CP violation is central to the matter-antimatter asymmetry.
Could the profound mysteries of antimatter and dark matter be linked?
Journal References:
- LHCb collaboration. Study of Λ0b and Ξ0b decays to Λh+h′− and evidence for CP violation in Λ0b→ΛK+K− decays. DOI: 10.48550/arXiv.2411.15441
- LHCb collaboration. First evidence for direct CP violation in beauty to charmonium decays. DOI: 10.48550/arXiv.2411.12178
