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The CERN Colloquium of T.D.Lee September 3, 2007

Posted by dorigo in news, personal, physics, science.
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The main auditorium hall at CERN (a larger one than the one which hosted Lisa Randall’s seminar the previous day, whose name I have not learned yet) was packed with maybe 400 people last Thursday afternoon. All had come to hear it from Tsung-Dao Lee, the co-discoverer of parity nonconservation in weak interactions, who gave a seminar in the fiftieth anniversary of his victory of the Nobel prize.

As the day before, I had not planned my attendance – I was expecting to leave CERN to Venice at about the same time. By car it is a 600 km trip, which I usually cover in a bit more than 5 hours, if all goes well. By leaving at four in the afternoon I would have a chance to be home at a very reasonable 9-ish PM, but the seminar was worth a delay.

T.D.Lee arrived fashionably late, when the buzz level in the auditorium had reached at least 70 or 80 decibels. He is still a handsome elderly figure, although he is well in his eighties (he was born in 1926). He wore a nice black jacket with golden buttons, a grey tie and brown trousers, and I would have given him 65 years of age, had I not known he is much older. He is clinging to much of his hair still, and most of what’s left is not even gray.

Funnily enough, despite his long absence from the arena (he noted at the start that CERN is timeless, by pointing to the two large round clocks hung on both sides of the vintage hall, both non-functioning: his last appearance here had been 18 years back), I had sort of interacted with him a couple of years ago, when I received a fax he wrote to support the research of a chinese physicist. But that is a story I already told.

Before I venture to summarize the contents of the colloquium, I wish to first briefly discuss their huge achievement, which is 50 years old but it still shines with pristine light as it shows how pure thought, and not even complex formulas, may be enough to reach the top. Let me quote from the presentation speech given in Stockholm in by prof. O.B.Klein:

“The starting-point of Lee and Yang in their revision of the whole question of right-left symmetry in elementary particle reactions were certain strange observations concerning a kind of new particles called K mesons, which looked as if they were in contrast with the assumption mentioned. Even if these observations puzzled greatly many physicists, it was only Lee and Yang who seriously took the consequences of them, in that they asked themselves what kind of experimental support there was for the assumption that all elementary particle processes are symmetric with respect to right and left. The result of their investigation was unexpected, namely that the validity of the symmetry assumption even in the best known processes had no experimental support whatsoever, the reason being that all experiments had been so arranged as to give the same result whether the assumption was valid or not. As if one had thought that Olav Tryggveson had his heart in the middle of the body because he was equally skilled with the left as with the right hand. Lee and Yang did not confine themselves to this negative statement but devised a number of experiments which would make it possible to test the right-left symmetry in different elementary particle transformations, and proposed them to their experimental colleagues.”

I intend to discuss in more detail elsewhere the whole history of this thrilling, revolutionary discovery, so here now I will just stress what Klein mentioned above: it was only Lee and Yang who took seriously the consequences of the “tau-theta puzzle” – as the riddle was named, after the two particles which looked the same but decayed to final states of opposite parity. And they won the house, because they were more disciplined, more skilled, and more imaginative. A lesson to be taught.

The presentation Lee gave was titled “Symmetry and Asymmetry in electroweak interaction”. It was by no means one of those commemorative seminars when one hears anecdotes and witty remarks on the atmosphere of a past discovery: not in the least! I do not know if I was the only one expecting a boring lecture, but for sure Tsung-Dao surprised me. After a very brief introduction centered on his hypothesis of parity violation in weak interactions and the confirmation by the experiment led by C.S.Wu, which allowed him to honor the memory of the chinese physicist, who died 10 years ago on February 17th, 1997, the seminar took a sharp turn.

Lee started by discussing how all known matter is made of 12 elementary particles. Of these, only electrons and muons were known 50 years ago. As for the neutrino, the one we knew back then was a mixture of those \nu_1, \nu_2, \nu_3 we know today. Science has made huge progress in these fifty years, but do we understand the two matrices that mix the leptons and the quarks, U_\nu and U_{CKM} ? They are the cornerstones of our particle physics. Each of them contains four relative phases, which are not measurable. So there are 12 masses and 8 phases in our model of matter. Do we understand them ? The answer, sadly, is still NO.

On the experimental side, the matrices have been measured quite well. For the neutrinos, we have not measured yet a complex phase (the measurement is not accurate enough to determine the imaginary part). So one has numbers available to test predictions. And Lee, together with R.Friedberg, used these numbers to try and understand if the matrices can be explained by a simple model. Their work is described in hep-ph/0705.4156.

I am not going to discuss in detail the description that Lee gave of his work, which you find in the link above; however, I will make an attempt at a summary. The starting observation for the work of Lee and Friedberg is that among the 12 fermions, which may be organized in four groups of three, each of those sets of three have one member of very small mass: they make up what is usually called “first generation”, u, d, \nu_1, e. Then there is the observation that CP violation, or equivalently, T violation, arises only by virtue of a complex phase in the mixing matrix. So one can take a step back and make a zeroth order approximation: assume all the mixing matrix elements are real, and in addition, ensure that there is a zero-mass eigenstate in each sector by imposing a hidden symmetry. The underlying motivation for doing so is twofold:

1) in a spontaneous T-violation theory, the inertia (higgs) field responsible for T violation can be the same field that generates the small masses of “zero mass” fermions, u, d, \nu_1, e.

2) T violation requires the existence of a reference frame that differentiates the sign of time flow. For a massive particle, this reference frame can simply be its rest frame.

Once one has set the stage with the initial unbroken theory, one can break the hidden symmetry and add a small T-invariance breaking term: both things can be achieved simultaneously by adding a phase factor e^{i \chi} in the interaction for each sector. One can then use the Jarlskog invariant J = (m_d m_s/m_b^2)^{1/2} A \lambda^3 cos (1/2 \chi) to verify the match between measured values of the quark mixing matrix U_{CKM} and the quark masses in this approximation, and one obtains a good match with experimental numbers. The same model fits the current knowledge of the neutrino sector very well too; however, further experimental input for neutrinos will clarify the matter more.

At the end of Lee’s talk, there were quite a few questions, but Lee was not intimidated ( wink). Here are a few:

Q: “You reminded us that higgs particle could be something like a cooper pair. The question is, do you have some suggestion on that ?” A: “Yes, I have a very good suggestion (for another talk)”. Laughs in the audience.

Q: “What value of the Wolfenstein parameter lambda can be extracted from your model ?” A: “In the expression for the J invariant, A and lambda are experimental values: the model is not predicting them, but using them as inputs.”

Q: “What about CPT violation ?” A: “Unlikely.” (Laughs in the audience)

Q: “(unintelligible mutterings from the back of the hall)”. A: “I do not understand your question, but the answer is no.” (More laughs).

Comments

1. Tripitaka - September 3, 2007

Beautiful post, thank you.

2. Tony Smith - September 3, 2007

Was there any further (formal or informal) discussion about Lee’s saying “… that higgs particle could be something like a cooper pair …” ?
In particular, was there any reference to the work of Yamawaki et al about Higgs as a T – Tbar condensate ?

Did Lee, in his “… very brief introduction centered on his hypothesis of parity violation in weak interactions …”, say much about his then-coworker Yang (who, as Lubos Motl said in a comment on another post in this blog, “… married … when he was 82 … she was 28 …”) ?

In their book “The Second Creation”, Crease and Mann say, about the “hypothesis of parity violation in weak interactions”:

“… In April 1956, Frank Yang attended the 1956 Rochester Conference … Feynman … and … Martin Block … a Duke experimenter … began quarreling about the theta-tau puzzle. At one point Block suggested that parity was not conserved … Feynman … was ready to say … “How stupid you are …” … by the time his jaw got over to the word “stupid” he thought a little bit … and said … “Well, maybe you have something there.” …
The last day of the conference … Feynman brought up a question of Block’s: Could it be that … parity is not conserved …
After that Yang said that he had looked at parity violation … without reaching a conclusion …
Block believes that his question at the Rochester Conference started the entire proces, and that the physics community does not recognize his contribution. …
Lee and Yang[‘s] … friendship was a casualty of their increasing celebrity. In 1962 they formally ended their decade-long collaboration. Physicists took care to invite one only when the oher was absent, and watched in distress when these two remarkable thinkers used the handsomely printed volumes of their collected works to attack each other. …”.

Was their any hint that they might have reconciled, or are they still far apart emotionally as residentially (Yang in China, Lee in USA) ?

Tony Smith

3. pechisbeque - September 3, 2007

Ditto!

4. dorigo - September 3, 2007

And I thank you both for your appreciation…

T.

5. moy01yom - September 3, 2007

I wonder to know why anyone is not going to point out that it is not politically correct to make commentaries about the color of the jacket’s buttons of elderly people. In my country it is not admisible at all !!!!

From Freedonia with love.

6. Quasar9 - September 4, 2007

Reminds me of those people who complain about the tv repeats at xmas. Hello, there’s a whole generation that has not seen them yet.
Have you seen the latest hollywood release, it’s yesterdays news if you’ve already seen the pre-release.

Yet we’ll go to a Shakespeare Play where they try to faithfully recreate something written hundreds of years ago, in some cases even going as far as using ‘ye olde english’

Or what about the pop and rock star, tired of singing his latest hit at a 101 venues or tv and radio shows. Can’t wait for his next song to be released. Perfectionists still strive to replicate the guitar work by Jimmy Page (Led Zeppelin) in Stairway to Heaven.

And we may choose to go to a concert where they still play Mozart or Bethoven, becaue it is culture – the Culture of an Age.

Medical Science promises us new miracle drugs & treatments every day, attempting to dazzle us with medical advances, in many cases trying to run before they can walk, in reality falling far short of their promises.

Theory and speculation grow exponentially every day. In the nano information age, we are suffering from information overload, there’s much talk of nanotechnology and quantum computing, but maybe science fiction is really still five hundred years away. Of course technological advances come in leaps and bounds, but theoretical advances and high energy physics cannot always be applied to the physical world (overnite).

To return to your question, there should be something new to add almost every day (as new data comes in at CERN) however whether it will be new physics that still remains to be seen. And if such a thing as TOE make an appearance or be revealed, then I guess we’ll be debating whether it is big toe or little toe we did get a glimpse of.

7. dorigo - September 4, 2007

Hi Tony,

yes, I know the story of Block and Feynman. The history of those years is very entertaining… It has been told by many of the actors in many different ways. I do think some merit is to be ascribed to Block, and even more to Feynman – who showed in that instance, too, his innate ability to grasp what were the really important questions.

As for your questions: the issue of the higgs as a tt condensate was not discussed at all, there was only a hint in his talk and a question I mentioned. Yang was not mentioned either.

Cheers,
T.

8. dorigo - September 4, 2007

yes moy01yom, I agree – it was a despicable fault to mention the buttons. I did it on purpose to offend your country😉

Cheers,
T.

9. dorigo - September 4, 2007

Hello quasar9,

although I agree with what you write, I have to say I failed to find a connection with the post of TDLee. What link am I overlooking ?

Cheers,
T.

10. Quasar9 - September 4, 2007

lol T, I can see why you were puzzled.
Seems I scrolled too fast and commented on the post below.
Though of course it applies to those who lecture copiously like Lee and Randall too, the comment was meant for the next post.
It’s always a funny thing copyright, plagiarism and even auto-plagiarism, when so much of what is written or said has been written or said before – yet, we still look for ways to give it a new flavour or twist, or even to take it to the next level and/or other dimensions.

11. Tumbledried - September 5, 2007

Hi Tommaso,

I must admit I find the idea of parity, charge, handedness, time etc violations very hard to understand intuitively, given my lack of education in this area, since I did nothing beyond a particle physics course in undergrad that I found largely incomprehensible. Is there any way of easily understanding, in a naive sort of way, what is going on with any of these things?

Best,
Tumbled

12. dorigo - September 5, 2007

Hi Tumbledried,

you are right, these ARE tough concepts. I have a plan to at least discuss parity violation in some detail in a post very soon, and make it understandable to non quantum-mechanically-aware readers. Today is not a good day for that, but stay tuned!

Cheers,
T.

13. dorigo - September 5, 2007

Hi Quasar9,

yes, after replying I looked again and I understood your previous comment. I can only add that I agree, nobody can be truly original anyway – if we leave aside those eureka moments when one has a pure thought that nobody had before. For sure not in a proceedings paper describing experimental results. We experimentalists are the blue-collar workers of HEP, and what is asked is to produce a summary of what we said at a talk – so I will just do that, and if I cut and paste a description of the detector I used elsewhere, well, who cares: the detector hasn’t changed either.

Cheers,
T.

14. Tumbledried - September 5, 2007

Thanks, I look forward to what you have to say.

Best,
Tumbled

15. Tony Smith - September 5, 2007

Tommaso said “… We experimentalists are the blue-collar workers of HEP …”.

Over on Peter Woit’s blog entry about the September 2007 Physics World article by Matthew Chalmers,
Peter Woit said “… Unlike you [Matthew], I [Peter] have a Ph.D. in the subject ..”.
When I pointed out that Matthew Chalmers did indeed have a Ph.D. in particle physics (from Glasgow University),
Peter Woit replied “… he [Matthew] does have a Ph.D, but in experimental, not theoretical particle physics …”.

I might expect such smug arrogance from superstring theorists, who have very little contact with experimental results,
but it is sad to see it in a non-superstring theorist.
Maybe it can be explained by Peter Woit being to some degree allied with LQG advocate Lee Smolin, and the current status of LQG being as distant from experimental results as superstring theory.

Tony Smith

PS – When did real physicists (i.e., those who do experiments) quit calling themselves “experimenters” and begin using the term “experimentalists” ?
Why ?

16. dorigo - September 5, 2007

Hi Tony,

as a woitino I have to defend Peter, of course. What
I think is that he was making some point by mentioning his background in particle physics, rather than looking down on Chalmers. The thread developed by his post was not the most pacific environment I have seen around lately, although it is quite normal in the debate on string theory.

As for the last question, I have no idea – maybe somebody else here has an answer ?

Cheers,
T.


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