CERN's LHC has seen matter-antimatter asymmetry, such as CP symmetry breaking and $B_s^0$ meson decay.

The universe produced about 1 part per billion excess of baryons over anti-baryons. My understanding is that at any given temperature there is no excess matter at thermodynamic equilibrium. Instead, the cooling universe creates non-equilibrium conditions.

Suppose there is a lower activation energy for $antibaryon \Leftrightarrow lepton+radiation$ than for $baryon \Leftrightarrow antilepton+radiation$. At high temperatures both reactions are in equilibrium. As the universe cools and the "radiation" (photons and low-mass particles) loses energy both equilibriums are driven forward. But as the universe keeps cooling the latter reaction is the first to "freeze out" (become kinetically inhibited) since it has higher activation energy. We are left with excess matter.

The quark gluon plasmas in CERN cool off far faster than they did in the Big Bang. I would presume that the rapid "quenching" means that the baryon asymmetry (production of excess protons/neutrons over antiprotons/antineutrons) could be far greater than in the early universe and therefore feasible to detect.

However, discussion of baryon asymmetry brings up so-called "grand unified theories" which live at ~10^12 times higher energy than CERN's LHC. Presumably this means that the "activation energy" of baryon-number violating reactions could be 10^16 GeV. But it is strange that the activation energy would exceed the mass of the reactants and products by so many orders of magnitude.

Has CERN observed excess creation of matter over antimatter? If not, are it's collisions too low energy to do so?


1 Answer 1


Producing a different amount of a particle versus its antiparticle is called "baryon number violation" or "lepton number violation". These are the terms to search for if you want to dive deeper.

As you suggest in you question, these are key ingredients to understanding the matter–antimatter asymmetry of the universe but, so far, they have not been observed: neither at CERN nor any other lab.

For a short (but quite technical) overview, see page 13 of https://pdg.lbl.gov/2022/reviews/rpp2022-rev-conservation-laws.pdf


Your Answer

By clicking “Post Your Answer”, you agree to our terms of service and acknowledge you have read our privacy policy.

Not the answer you're looking for? Browse other questions tagged or ask your own question.