Physicists have long been puzzled by the question: how could our universe ever have evolved to include stars, galaxies, and humanity? According to theory, during the Big Bang, matter and antimatter should have been created in equal quantities and annihilated. But this did not happen, resulting in the universe we observe. Antimatter almost disappeared from our world, while ordinary matter remained and formed everything tangible in it. So what went wrong?
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According to generally accepted theories and numerous experimental data, matter and antimatter differ only in the signs of their charge. Accordingly, they obey the so-called CP symmetry (combined parity). Simply put, if the charge of all particles in the entire Universe were changed and their spatial coordinates were inverted – a kind of mirror Universe made of antimatter – then the laws of physics would not change. However, this is true only if particles and antiparticles differ only in the sign of their charge. And yet, such an explanation does not take into account the absence of antimatter in the observable Universe.
If signs of CP symmetry violation are found, this could explain why there are not equal amounts of matter and antimatter and what other differences, still hidden from us, exist between them.
Signs of CP-symmetry violation in mesons (fermions) were first discovered in 1964, for which the Nobel Prize in Physics was awarded in 1980. However, for baryons, which make up the vast majority of visible matter in the Universe (primarily neutrons and protons), such signs had not been recorded until recently. Their discovery would be a decisive step towards explaining the “asymmetrical” Universe.
That is, until late March 2025, when CERN officially announced that it had obtained statistically significant evidence for CP violation for baryon-family particles. Physicists from the LHCb collaboration had studied data from the first two runs of experiments at the Large Hadron Collider (LHC). They were looking for differences in the decay rates of particles and antiparticles, such as the beautiful lambda baryons (Λb). If these particles were identical in everything except the sign of their charge, there would be no difference in their decay rates.
The researchers analyzed 80,000 decays recorded during LHC missions between 2009 and 2018. They found a 2.45% difference between matter and antimatter decays. That’s 5.2 standard deviations (sigma), which is significant enough to consider the observation of CP violation a scientific discovery.
«”The reason it took longer to detect CP violation in baryons than in mesons is the size of the effect and the amount of data available,” explained LHCb collaborator Vincenzo Vagnoni. “We needed a facility like the Large Hadron Collider that could produce enough beauty baryons and their antiparticles, and an experiment that could accurately determine their decay products.”
«The more systems in which we observe CP symmetry violation, and the more accurate the measurements, the more opportunities we have to test the Standard Model and search for physics beyond it,” the scientist added.