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Lecture 1 November 27, 2007

Posted by dorigo in language, personal, physics, science.

Today was the first day of my course in subnuclear physics in Padova. I had given similar lectures in the past -to PhD students, both in Padova and in Catania- but I felt more responsibility this time, partly because I was going to discuss basic concepts of particle physics to students that had not had prior exposure to them.

The lecture I gave today was about the need for gauge symmetries, the lagrangian formalism for scalar and fermion fields, the issue of endowing with mass the bosons mediating weak interactions, and the connected problems of divergences and renormalizability. It was a fairly theoretical discussion, although I tried to give as much experimental perspective as I could to the various issues treated. I tried to make it quite clear just why one needs to insist that a lagrangian function retain local gauge invariance, and on the other hand why it is mandatory to add terms that at first glance spoil the invariance. I spent some time also describing the connection between observed and only hypothesized weak processes, their divergent behavior, the need for neutral vector bosons, and the resulting predictions of the GSW theory. The next lesson will start with the Higgs mechanism.

I was a bit worried before the lecture – I usually keep a cool mind in such occasions, but admittedly my knowledge of the theoretical nuisances below the surface of the simplified treatment I offered  in the lecture is not very deep. What worried me was not the chance of incurring in a tough question I was unable to answer – I have no trouble admitting my ignorance if that is the case- so much as the risk of embarking in a discussion of details which I would have explained in a less than satisfactory, inaccurate way: the responsibility of writing garbled physics concepts on the clean slates of my students’ minds. I have to admit I did not sleep well last night: but I prefer to ascribe that to my jetlag, and to Ilaria’s contribution -she woke everybody up at 4 in the morning with symptoms of a flu.

I did well. I recorded myself, and later analyzed the recording by noticing how much time I had spent on several topics, how repetitive I had been on some issues, and how clearly I had expressed the most important concepts. Overall I am mildly satisfied with the result. One thing I noticed, though, is that I have a mannerism in my speech, which consists in interspersing a sound like “errrr…” between sentences when I am thinking at what to say. I should just silence myself during those short, 1-second intervals. I will be working at that in the next lectures… Room for improvement there.

The next lesson will be the hardest for me, since the full theoretical formalism of the Standard Model will be explained in its details, and I will take care to derive a few important consequences for vector boson and Higgs phenomenology, and the shortcomings of the theory. From then on, I will start delving with the phenomenology of Higgs production and decay at colliders, things on which it will be much easier for me to produce a decent lecture. Following that, I will discuss top quark physics and other topics in hadron collider physics at the Tevatron and the LHC. I believe my students will also be happier with the latter part of the course…



1. Kea - November 27, 2007

The next lesson will be the hardest for me, since the full theoretical formalism of the Standard Model will be explained in its details…

Goodness, how on earth can you pack so much into a lecture? Is this a QFT-in-a-week course?

2. dorigo - November 27, 2007

Hi Kea,

well, not a week. The full course spans 48 hours of lectures. Of the 12 I am assigned, I will spend 6 on the Higgs sector of the SM. The students are supposed to know from previous courses the basics of field theory – stuff like the dirac and klein-gordon equations, the euler-lagrange equations and noether’s theorem. By the time they got to my part they should also have learned about weak interactions, v-a, phenomenology of the latter, deep inelastic scattering, a little of this and a little of that…

However, I admit that doing in 6 hours the Higgs mechanism (which I introduced today by discussing goldstone’s theorem and the other things) and the SM lagrangian, plus the fermion and boson masses, the interactions ,and a few things about Higgs boson phenomenology, plus searches at colliders, is a bit of a stretch. The quality of undergrad courses, I think, has lowered a bit in the last few years, because of the need of the italian university system to equalize with other european systems. I am sorry to sound like the classical embittered old guy who can only criticize how things have got rotten, but when I did my undergrad studies, one learnt physics in four years of courses, which most of the students completed in seven (the average, in Padova). Now, because of european standards, a laurea lasts 3 years and a specialization laurea 2 more. Which means that in five years students are done. All of them – the average length of total studies is less than 6 years. So there is more than one year of decrease in the duration of studies. This of course has nothing to do with the intelligence or efficiency of students themselves, so it has to do with the level of courses imparted….


3. Kea - November 27, 2007

This is happening not only in Italy. Here the courses are much more watered down than when I was an undergrad 20 years ago. Heck, many 17 year olds can’t even do basic algebra any more, so they can hardly be expected to derive formulae in an exam.

4. Nick - November 28, 2007

So, can we see your lecture video? 🙂

5. dorigo - November 28, 2007

Hi Nick,
no, I only took the audio recording… And it is in italian, so it is of little use to most of the visitors here. The slides are in italian too. I realized that was a mistake as I learned that there was one Erasmus student (exchange visitor from a foreign university) in my audience, who does not speak italian fluently and would have benefitted from slides in English (I offered to do the discussion in English, but that would have let down a few others).

In any case, I am considering a quick translation of the slides. Maybe during xmas holidays… In that case I could post them here, but I do not think they would represent any breakthrough in the availability of easy study material on the web – there is already a lot of good material around.


6. Fred - November 28, 2007

Prof. T.

1. How much of an input do you have in determining the guidelines, content and material for your course?
2. Are text books and publications assigned along with your lectures?
3. What kind of visual aides are used during class?
4. Are certain words, phrases, or concepts spoken in a language other than Italian? For instance, there are a number of words in philosophy which are more appropriately understood in German.
4. Have you ever given a course to English speaking students?
5. Do you ask your students to visit this website?

7. Tony Smith - November 28, 2007

Will you have a pdf of your slides ?
Your “La Fiszica delle Particelle Elementari”
slides are both great and in Italian.

Tony Smith

8. dorigo - November 28, 2007

Hi Fred,
unfortunately it looks like I will never be a professor, since two years ago, when there were openings for research positions both in the university and in INFN, I was diverted into INFN by a subtle manouver inside my Department. From then on, switching horses has been declared not kosher… At least for a while.
Anyway, I was able to decide freely the details, but I am responsible only for a quarter of the whole course this year, and so I am constrained to discuss some topics which the course can’t miss. Within the broad boundaries of “Higgs sector of the SM” and “heavy flavor physics at colliders” I could decide what to present and what to neglect.
I based the theoretical part of my lectures on a few books I chose for their clarity, but the students are not required to study the matter there. Three texts are dear to me: Halzen,Martin “Quarks and Leptons…”, and Burcham, Jobes “Nuclear and Particle Physics”, plus Ellis,Stirling, “QCD and Collider Physics”.
I use powerpoint slides and my own scribblings on the blackboard (which I found out I am drawn to use much more than I thought).
I speak italian, but things such as “bremsstrahlung”, “gauge”, “branching ratio”, “collider”, “minimum bias”, “underlying event”, “initial state radiation” stay in their original language.
I never gave courses to English students, although I did a couple of seminars to Harvard students (one on V-A, one on the physics of rainbows).
No, I did not ask them to visit… But I did add the web site address to my list of contacts.


9. dorigo - November 28, 2007

Hi Tony,

well, yes, I can make the slides available, although that means increasing exponentially the chance that I’m proven wrong somewhere. Criticism can only improve me, however, so I think I’ll do it…


10. Andrea Giammanco - November 28, 2007

I gave two lessons recently (to francophone students, but in english – they studied it a lot in the previous years, something that I doubt is true in italian universities, even with the new system) about the J/psi discovery, starting from the Cabibbo angle and going through the GIM mechanism. I enjoyed a lot to explain the theoretical part, but I was also frightened to be judged too imprecise on that side (and on the other hand I had to be easily understandable, and quick). Luckily, they seemed happy with the level that I chose.
My next lesson will be about the W and Z discovery, and in the theoretical introduction I would like to explain that the W and Z masses were not completely unknown at that time, being already quite constrained around 80-90 GeV.
Problem: I absolutely can’t remember what was constraining them! 🙂 (Apart from the ratio of the two, known from the Weinberg angle which had been already measured.)
Can you help me?

(Ahah I feel like cheating during a homework!)

11. dorigo - November 28, 2007

Hi Andrea,

I can answer that – it is slide 28 in my course, I will discuss it tomorrow :). Apart from theta_W, known by then by neutrino scattering experiments, one could use the measured rate of muon decay to get G_F, and from the unification of electroweak couplings g \sin \theta_W=e and the measured value of the fine structure constant \alpha=e^2/4\pi could then obtain everything: first v (the vacuum expectation value of the Higgs field) is known by substituting the W mass, which in the SU(2)xU(1) broken lagrangian is expressed as m_W=1/2 gv, in the expression equating the low- and high-energy behavior of weak charged currents, g^2/8m^2_W=G_F/\sqrt 2, to get v=246 GeV. Then one can get m^2_W=  (\alpha \pi / G \sqrt 2)/ \sin^2 \theta_W. Thus one got an estimate of about 78.3 GeV with 2.5 GeV errors, and 89 GeV for the Z.


12. Andrea Giammanco - November 28, 2007

True, thanks a lot! I was not thinking that G_F is related to the W mass through g, and g is known once you know the Weinberg angle.
I will have a look at your slide immediately.

13. jcn - November 28, 2007

“One thing I noticed, though, is that I have a mannerism in my speech, which consists in interspersing a sound like “errrr…” between sentences when I am thinking at what to say. I should just silence myself during those short, 1-second intervals.”

i don’t know. if someone holding a lecture is pausing too long without any sound, i get irritated. i don’t mind people filling gaps between sentences with all kinds of syllables, as long as they keep making a noise.

14. dorigo - November 28, 2007

JCN, that’s a nice encouragement, thank you 🙂 I remember one very awkward feeling when Stephen Hawking’s PC had to reboot during his lecture at a Cosmology conference. 5 minutes with nothing to do but stare at a wheelchair and a poor soul struggling with his synthetic exoskeleton.


15. Andrea Giammanco - November 30, 2007
16. dorigo - November 30, 2007

Andrea, that’s a stab in the back 🙂
I think my slides fail on every count according to the guidelines in your link… But there is a rationale for that. My students will have to pass an exam! So they are simply bound to love and cherish what I showed them, no matter what 😉


17. Slides for lectures 3 and 4 « A Quantum Diaries Survivor - December 5, 2007

[…] – and to know what I am talking about see https://dorigo.wordpress.com/2007/11/27/lecture-1/here). In this segment of the course, I discussed Higgs boson phenomenology and its searches at […]

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