Sorry. Check your PMs.

Thanks. I'll look at it as soon as I have Adobe reader 11...

Basically the two Nature articles (it is, in fact, two articles by physicists at the University of Massachusetts and at University College London) explain that a pear-shaped nucleus would tend to amplify a permanent electric dipole moment (EDM), if the nucleus had one in the first place. This would be significant, because the existence of a permanent EDM would break time symmetry as explained here:

To see why an EDM violates T symmetry, one has to consider the fact that a particle generally has a magnetic dipole moment (MDM), which can be thought of as being due to a tiny current flowing in a circle, or to the particle spinning. And there is a contribution to the particle’s energy that depends on the relative alignment of the EDM and the MDM. If T is reversed, the current flows in the opposite direction, so the MDM changes direction. But the EDM remains unchanged. So the alignment between the two has changed, the energy has changed and the symmetry is broken.

and if time symmetry is broken, then so must CP symmetry be (charge and parity), so that the whole system overall is CPT invariant. And CP asymmetry would, in turn, help in accounting for the overwhelming matter-antimatter asymmetry that we observe.

Evolving wrote:Basically the two Nature articles (it is, in fact, two articles by physicists at the University of Massachusetts and at University College London) explain that a pear-shaped nucleus would tend to amplify a permanent electric dipole moment (EDM), if the nucleus had one in the first place. This would be significant, because the existence of a permanent EDM would break time symmetry as explained here:

To see why an EDM violates T symmetry, one has to consider the fact that a particle generally has a magnetic dipole moment (MDM), which can be thought of as being due to a tiny current flowing in a circle, or to the particle spinning. And there is a contribution to the particle’s energy that depends on the relative alignment of the EDM and the MDM. If T is reversed, the current flows in the opposite direction, so the MDM changes direction. But the EDM remains unchanged. So the alignment between the two has changed, the energy has changed and the symmetry is broken.

and if time symmetry is broken, then so must CP symmetry be (charge and parity), so that the whole system overall is CPT invariant. And CP asymmetry would, in turn, help in accounting for the overwhelming matter-antimatter asymmetry that we observe.

The odd thing about CP symmetry is that slight vioations of it are considered acceptable, as long as CPT symmetry remains intact. Could that be purely because it was long ago found that the electro-weak interaction violated CP, and nobody thought it odd?

I don't know about acceptable, but the point being made in the second article (which I hope you'll be able to read soon!) is that the CP asymmetry provided for in the standard model is nowhere near enough to account for the fact that the universe seems to consist almost entirely of matter, as opposed to anti-matter (well - the matter part of it does!).

When B mesons decay (B mesons are mesons composed of a bottom antiquark and either an up, down, strange or charm quark) but do not take the charm route, a matter/anti-matter asymmetry (CP violation) is known. In one of the possible channels, the asymmetry is observed to be the largest yet seen (>70%). No one seems to be too excited about this because earlier QCD calculations predicted that this should indeed be the case - the strong (QCD) force is messing with weak SU(2) force interactions at these energies and Evolving's post^ still stands.

Magic beauty charmless decays
By admin
MAR 17, 2022

The largest CP violation ever observed.

Today, at the Rencontres de Moriond EW, and on Tuesday, during a CERN seminar, the LHCb Collaboration reported the results of measurements of CP asymmetry in the charged charmless B meson decays into three light mesons. In these decays the b-quark is transformed into a u, d or s-quark instead of its dominant transition into a charm c-quark (therefore the decays are “charmless”).

...continues @ LHCb link

In a specific kinematical region of the B±→π±π+π– decay, defined in the seminar and Moriond presentations, the CP asymmetry is as high as 75%, see the image to the left above. This is the largest CP violation ever observed.

Here’s a question that I never considered before because I understand what it means colloquially but not in Quantum Physics.

What does decay actually mean in QR?


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Quantum mechanical states are energetic and it appears nature prefers to be in the lowest possible mass/energy state it can achieve after interaction - a ball rolls downhill as its potential energy gets converted to kinetic energy that is then dissipated by friction in the system, for example.

Apart from protons, most decays lead to stable 'elementary' states - those with no constituents (as far as we can tell hitherto) - like electrons, neutrinos and photons. The B meson decays to pions discussed above are not the end of the story as the pions will decay in short time to muons and eventually electrons, and neutrinos.

Edit to include that the final states are also those with the lowest possible mass - electrons & neutrinos are the lightest in their families and photons are energetic but massless.

Quantitatively:

Thank you for that straightforward explanation.


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