New Antimatter Physics Discovered at the Large Hadron Collider
7 comments
·July 20, 2025pdonis
musicale
> as is unfortunately common now with Scientific American
Sad but true, and something I've been noticing as well.
gus_massa
Let's use the opportunity to ask technical questions / confirm my interpretation...
When I was young, nobody was sure if the https://en.wikipedia.org/wiki/Cabibbo%E2%80%93Kobayashi%E2%8... was real or complex. IIUC Wikipedia, now it's confirmed to be complex!!! [1]
The CP (charge-parity) symmetry is interesting, because if it is broken it means that the T (time) symmetry is also broken. In Quantum Mechanics if the operator to calculate the energy is real, then the system is invariant if you magically change the variable t to -t, this is call time inversion, that sounds cool but it's just a mathematical trick and not a device to travel back in time.
So a complex Cabibbo–Kobayashi–Maskawa matrix ensure there is a "problem" when you change t to -t and this indirectly may explain why if the initial universe has the same amount of matter than antimatter, now it's not balanced.
If I can continue with some speculations because my handwaving is not strong enough ... In https://www.nature.com/articles/s41586-025-09119-3/figures/1
* in the top diagram a bottom quark transforms into a up quark, and W- particle, and then the W- particle decays into a strange and anti-up quark. This transformations uses 1 or 2 of the coefficients of the matrix.
* in the bottom diagram, there is an intermediate top quark, but after more interactions the result is the same. But the top quark here forces to use the others coefficients of the matrix. So the result has not only a different amplitude, but it's also complex!!! [1]
For the final result you must combine both diagrams and also a standard complex phase caused by the advance of time, something like |A*e^{itm}+B|^2. When you replace t with -t, the sign of the phase changes. If both diagrams had real amplitudes A and B it doesn't matter because |A*e^{-itm}+B|^2.
But if A is real and B=b+ci then |A*e^{itm}+b+ci|^2 is different of |A*e^{-itm}+b+ci|^2 and you get an asymmetry.
Is this correct? Anything to add/remove/rewrite?
[1] Sorry fo the exclamations marks. Nobody told me. 68.8°±4.5° is a lot. It's not slightly complex, it's very complex.
MengerSponge
i => -i under T. If you want to read even more, time reversal is an antiunitary transformation. (That's the magic phrase to anchor your searches)
Physics is built on symmetries. They're how we can multiply the predictive power of simple theories. Time-reversal is fun and important, but it isn't actually about reversing time. It's about understanding the symmetry governing the interactions that define our existence.
PaulHoule
A big deal.
One of the outstanding mysteries of particle physics is why there is so much matter in the universe but practically no antimatter.
The mainstream explanation is that there is a big matter/antimatter asymmetry in the lepton sector, say involving neutrinos, and this imbalance is transmitted to the hadron sector through
https://en.wikipedia.org/wiki/Sphaleron [1]
and it is the hadron sector that matters because it has almost all the mass. If there is a strong enough asymmetry between hadrons though, that might be sufficient to explain the imbalance.
[1] not "physics beyond the standard model" but something like the Higgs boson which is predicted by it!
terminalbraid
How do I reconcile your claim that this news is "A big deal" with respect to the matter-antimatter asymmetry when the article states plainly
"This puny amount of CP violation, however, cannot account for the profound asymmetry between matter and antimatter we see throughout space."
and
"The observed CP violation seems to be in line with what has been measured before in the quark sector, and we know that is not enough to produce the observed baryon asymmetry."
?
The title is clickbait (as is unfortunately common now with Scientific American). This is not "mysterious"--CP violation is expected according to the Standard Model, it just hasn't been observed in baryons before, only in mesons, as the actual Nature paper [1] makes clear.
[1] https://www.nature.com/articles/s41586-025-09119-3