Using the largest sample yet of particles called beauty mesons, physicists with the CMS Collaboration at CERN’s Large Hadron Collider (LHC) refined a decades-old test of the subtle imbalance that let our Universe exist at all.
Neutral beauty mesons can turn into their own antimatter opposite and back again. Image credit: Ansar Iqbal / CMS.
One of the greatest mysteries in physics is why the Universe is made almost entirely of the normal matter that forms us and everything we touch.
Every matter particle has a corresponding antiparticle with the same mass but the opposite charge and, according to our best theories, the Big Bang should have produced matter and antimatter in nearly equal amounts. Today, however, almost no antimatter remains.
In their new paper, the CMS physicists explored one ingredient that could help to explain this imbalance, a subtle difference in the behavior of matter and antimatter known as charge-parity (CP) violation.
“Studying neutral beauty mesons, which are made of a beauty antiquark and a down-type quark, is one of the best ways to investigate CP violation,” they explained.
“This is because neutral beauty mesons have a remarkable property — they can spontaneously transform into their own antiparticles and back again.”
By measuring the tiny difference in how often matter and antimatter versions of these particles decay over time, we can test the Standard Model with unprecedented precision.”
The researchers analyzed proton-proton collision data collected between 2022 and 2025, reconstructing specific decays of about 1.4 million B0 mesons, which contain a down quark, and 16,000 B0s mesons, which contain a strange quark.
A key challenge was determining the type of each meson at the moment it was produced, before it decayed into a J/ψ meson and a neutral kaon.
To achieve this, the scientists employed an algorithm based on state-of-the-art artificial intelligence.
The system combines information from muons, electrons, jets associated with a collision event and, for the B0s meson, nearby particles produced in the collision.
This significantly improved the experiment’s ability to identify the meson’s initial state compared to previous analyses.
“The measured CP violation is in line with the predictions of the Standard Model, and includes the most precise measurement to date of CP violation in the decay of a B0s particle into a J/ψ meson and a neutral kaon,” they said.
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CMS Collaboration. 2026. Measurement of time-dependent CP violation in B0(s)→J/ψK0S decays with the CMS detector. CMS-PAS-BPH-26-005
