How the modern universe is primarily composed of matter and not antimatter has foxed astrophysicists for decades, but a result from a Large Hadron Collider (LHC) experiment has uncovered a new clue behind the matter-antimatter asymmetry mystery.
During high-energy proton collisions in 2011, the worlds most powerful particle accelerator, located at the France-Swiss border near Geneva, created BOs mesons — hadronic subatomic particles comprised of one quark and one antiquark — inside the LHCb experiment.
By observing the rapid decay of the BOs, physicists were able to identify the neutral particle’s decay products — i.e. the particles that it decayed into. After a huge number of proton collisions and BOs decay events, physicists have announced that more matter particles are generated than antimatter during neutral BOs decays.
“The discovery of the asymmetric behavior in the BOs particle comes with a significance of more than 5 sigma — a result that was only possible thanks to the large amount of data provided by the LHC and to the LHCb detector’s particle identification capabilities,” Pierluigi Campana, spokesperson for the LHCb collaboration, said in a CERN announcementon Wednesday (April 24). “Experiments elsewhere have not been in a position to accumulate a large enough number of BOs decays.” 5-sigma is the statistical “gold standard” of a discovery in particle physics.
This preference of matter over antimatter in decay products of particles is known as a “CP violation.” Generally, the laws of physics will only allow equal quantities of matter and antimatter to be produced in decay events (called “CP symmetry”). However, there are some exceptions known within the Standard Model of physics.
Violation of CP symmetry was first documented in the 1960s in the decay of neutral kaon particles. Since then, Japanese and US labs have detected CP violation in BO mesons. Recently, the LHCb experiment has detected CP violation in B+ mesons. And now, the decay of BOs is showing similar behavior.
At the time of the Big Bang, it is thought that equal quantities of matter and antimatter were created, but how did matter overwhelm antimatter to form the universe we know and love today? Although the effect of a slight asymmetry in BOs decay products is suggestive, the effect is very small, but it is another clue as to why the nature of our universe prefers matter over antimatter.
“We also know that the total effects induced by Standard Model CP violation are too small to account for the matter-dominated universe,” said Campana. “However, by studying these CP violation effects we are looking for the missing pieces of the puzzle, which provide stringent tests of the theory and are a sensitive probe for revealing the presence of physics beyond the Standard Model.”
The LHCb group has submitted a paper to the journal Physical Review Letters. A preprint of the paper can be downloaded from the arXiv service.
Image credit: Corbis