[HN Gopher] New Antimatter Physics Discovered at the Large Hadro...
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New Antimatter Physics Discovered at the Large Hadron Collider
Author : Bluestein
Score : 38 points
Date : 2025-07-20 18:21 UTC (4 hours ago)
(HTM) web link (www.scientificamerican.com)
(TXT) w3m dump (www.scientificamerican.com)
| cmrx64 wrote:
| https://archive.ph/a7VB3
| pdonis wrote:
| 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
| gus_massa wrote:
| 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.
| 68.8deg+-4.5deg is a lot. It's not slightly complex, it's very
| complex.
| MengerSponge wrote:
| 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.
| musicale wrote:
| > as is unfortunately common now with Scientific American
|
| This is something I've noticed as well. I'm not sure when it
| started, but it seems to have gotten worse.
| PaulHoule wrote:
| 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 wrote:
| 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."
|
| ?
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