CP Violation in D Meson Decay

LHCb is reporting the first evidence of CP violation in the decay of D meson.

The D⁰ meson is made of a charm quark and an up antiquark. So far, CP violation has only been observed in particles containing a strange or a bottom quark. These observations have confirmed the pattern of CP violation described in the Standard Model by the so-called Cabibbo-Kobayashi-Maskawa (CKM) mixing matrix, which characterises how quarks of different types transform into each other via weak interactions. The deep origin of the CKM matrix, and the quest for additional sources and manifestations of CP violation, are among the big open questions of particle physics. The discovery of CP violation in the D⁰ meson is the first evidence of this asymmetry for the charm quark, adding new elements to the exploration of these questions.

If confirmed, this will be another meson that has exhibited such CP violation, and adds to the argument that such symmetry violation could be the source of our matter-antimatter asymmetry in this universe.

CP violation is an essential feature of our universe, necessary to induce the processes that, following the Big Bang, established the abundance of matter over antimatter that we observe in the present-day universe. The size of CP violation observed so far in Standard Model interactions, however, is too small to account for the present-day matter–antimatter imbalance, suggesting the existence of additional as-yet-unknown sources of CP violation.

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Noether Theorem And Symmetries

This is not something new that I'm highlighting on this blog. I've mentioned a link to Emmy Noether theorem before in this post, and also highlighted a history of her work here. However, I think that there is no such thing as too much publicity on Emmy Noether, because she deserves to be remembered and admired through eternity for her accomplishments and insights.

This video tries to explain the significance of her work connecting conservation laws with symmetry principles.



However, I think that if I were a layperson, I'd miss the important point in this video. So here is the takeaway message if you want one:

Everything that we see and every behavior of our universe can be traced to some conservation laws. Each conservation law is a manifestation of some underlying symmetry of our universe.

This is the insight, and a very important insight, that Noether brought to the table, and it was revolutionary to physics. These symmetries are what we currently have as the most fundamental description of the universe that we live in.

Watch this video, and read the links that I gave above, several times if you must, because you owe it to yourself to know about this person and her immense effect on our understanding of our world.

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Grandfather Paradox - Resolved?

This Minute Physics video claims to have "resolved" the infamous grandfather paradox. Well, OK, they don't actually say that, but they basically indicated why this might be a never-ending loop.



Still, let's think about it this way instead. During your grandfather's time, presumably, ALL the atoms or energy that will make you are already there, only they are all not together to form you. This only happens later on. But they are all there!

But here you come along from another time, popping into existence in your grandfather's time. Aren't you violating conservation of energy by adding MORE energy to the universe that are not accounted for? Now, unless there is a quid pro quo, where an equal amount of energy in your grandfather's time was siphoned to the future where you came from, this violation of conservation of energy is hard to explain away, especially if you invoke Noether's theorem.

I haven't come across a popular account of this issue.

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Symmetry And Higgs Physics Via Economic Analogy?

Juan Maldacena is trying to do the impossible: explain the symmetry principles and the Higgs mechanism using analogies that one would find in economics.

I'm not making this up! :)

If you follow the link above, you will get the actual paper, which is an Open Access article. Read for yourself! :)

I am not sure if non-physicists will be able to understand it. If you are a non-physicist, and you went through the entire paper, let me know! I'm curious.

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Checking On Antimatter

This is a rather nice, short summary on the study of anti-atoms, and in particular, CERN's effort to study the properties of anti-hydrogen and why it is so important.

With a big enough sample of anti-hydrogen, one can make detailed studies of the energy levels that the positron can occupy in its journey around the antiproton. These energy levels have been measured very precisely for hydrogen, and the expectation is that they should be identical in antihydrogen. But we won’t know until we look.
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The symmetry principle which these experiments are designed to test is whether physics, and therefore the whole universe, would look the same if we simultaneously swapped all matter for antimatter, left for right, and backwards in time for forwards in time. This is called a CPT (Charge/Parity/Time) inversion. The Standard Model of physics, and almost all variants on it, require that indeed the universe would be identical after such an inversion.

Now pay attention, kids. In physics, even when some of our most cherished theories have been used, and known to be valid, we STILL go out and test out many of its predictions. Here, the Standard Model says that antihydrogen should behave the same way as hydrogen. While the Standard Model certainly has been useful, and has been correct in many aspects, we do not simply accept its predictions for the behavior of antihydrogen. We still want to test it! In fact, many physicists are hoping that we see something the Standard Model can't explain, that something "weird" is going on that might give hints of new physics. This is what many of us in this field look gleefully for!

This is how science works. We verify an idea, a theory, etc., but we continue to test its RANGE OF VALIDITY, i.e. how far out does this thing work? It works here, but does it work there? It works when you do this, but does it work when you do that? This is how we expand the boundaries of our knowledge.

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Antiproton's Magnetic Moment Upholds CPT Symmetry

An amazing new measurement of the antiproton's magnetic moment by the ATRAP collaboration has improved the accuracy of the measurement its magnetic moment by 3 orders of magnitude. The new measurement agrees with the proton's magnetic moment to within the experimental error, thus still upholding the CPT symmetry.

The ATRAP Collaboration enters the fray with their own test for CPT violation. They look for a difference in the magnetic moments of the proton and antiproton. To enable this test, they precisely measure the magnetic moment of a single, trapped antiproton, achieving the most sensitive measurement to date of this quantity. They compare their result to the known value of the proton’s magnetic moment and find that the magnitudes are equal within experimental uncertainty, as predicted by the CPT theorem. 

The link above gives you free access to the paper.

Still haven't found anything yet that clearly violates the CPT symmetry.

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CPT

Finally, A Direct Detection Of Time Reversal Symmetry Violation In Elementary Particles?

It appears that we now have evidence of a direct detection of time reversal symmetry violation in elementary particles. This detection appears to be clearer and less ambiguous than before, and doesn't rely on the detection of CP violation.

It also seems that this is a result out of BaBar, which came from SLAC's linear collider before it was permanently shut down and converted into the LCLS. So that old gal is still giving us results from her grave!

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Brief Biography of Emmy Noether

To celebrate her 130th birthday this month, the NY Times has an informative biography of "The Mighty Mathematician You’ve Never Heard Of" - Emmy Noether (read it quickly before it is no longer available for free online).

Of course, to many of us in physics and mathematics, her name is quite familiar, and if you need a concise reason why she is so important in physics, this description of the Noether theorem would settle the case:

What the revolutionary theorem says, in cartoon essence, is the following: Wherever you find some sort of symmetry in nature, some predictability or homogeneity of parts, you’ll find lurking in the background a corresponding conservation — of momentum, electric charge, energy or the like. If a bicycle wheel is radially symmetric, if you can spin it on its axis and it still looks the same in all directions, well, then, that symmetric translation must yield a corresponding conservation. By applying the principles and calculations embodied in Noether’s theorem, you’ll see that it is angular momentum, the Newtonian impulse that keeps bicyclists upright and on the move.

I continue to be amazed at many of these women scientists and mathematicians who, despite all they had to endure during the times that they lived in, were able to persevere and produce such profound body of work. It is amazing enough to produce these amazing work. But considering that these women had so many social obstacles that the men didn't have, one can't help be impressed by what they had accomplished.

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Matter-Antimatter Asymmetry

This is an excellent article on the matter-antimatter asymmetry. It reviews the latest paper on decay asymmetry of the charm and anticharm mesons, but in the process, provided quite a good coverage of the progress in understanding why our universe is overwhelmingly lacking of antimatter.

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E. Noether's Discovery of the Deep Connection Between Symmetries and Conservation Laws

OK, this is not new. This arXiv manuscript was uploaded way back in 1998. But I was looking for some reference for someone else regarding the historical development of Noether's theorem, and stumbled upon this. It gives that, and also the significance of Noether's amazing insight. In fact, if you have not been aware of the importance of symmetries and how they reflect the conservation laws that we have, this is a good paper to read.

Abstract: Emmy Noether proved two deep theorems, and their converses, on the connection between symmetries and conservation laws. Because these theorems are not in the mainstream of her scholarly work, which was the development of modern abstract algebra, it is of some historical interest to examine how she came to make these discoveries. The present paper is an historical account of the circumstances in which she discovered and proved these theorems which physicists refer to collectively as Noether's Theorem. The work was done soon after Hilbert's discovery of the variational principle which gives the field equations of general relativity. The failure of local energy conservation in the general theory was a problem that concerned people at that time, among them David Hilbert, Felix Klein, and Albert Einstein. Noether's theorems solved this problem. With her characteristically deep insight and thorough analysis, in solving that problem she discovered very general theorems that have profoundly influenced modern physics.

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