## An exam in Subnuclear Physics January 9, 2009

Posted by dorigo in physics.
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Here are the questions asked at an exam in Subnuclear Physics this morning:

• Draw the strong and electromagnetic coupling constants as a function of $Q^2$, explain their functional dependence using feynman graphs of the corrections to the photon and gluon propagators, write their formula, and compute the value of the constants at $Q^2=M_Z^2$, given the values at $Q^2=1 MeV^2$ (QED) and $Q^2=1 GeV^2$ (QCD).
• The GIM mechanism: explain the need for a fourth quark using box diagrams of kaon decays to muon pairs. How does the charm contribution depend on its mass ? What conclusion could be drawn by that dependence in the case of B mixing measurements in the eighties ?
• Discuss a measurement of the top quark mass. For a dileptonic decay of top quark pairs, discuss the final state and its production rate.
• Discuss decay modes of W bosons and their branching fraction values. Discuss decay modes of Z bosons and their branching fraction values.

The student answered well all questions and he got 30/30 points.

1. Luboš Motl - January 9, 2009

Was she a graduate or undergraduate student? At any rate, you should tell her that she may become a string theorist now! 😉

dorigo - January 9, 2009

Not a she Lubos. Anyway he’s graduating on gravitational waves. I doubt he has any interest in string theory. Of course, Padova does have some addicts…

Cheers,
T.

2. Andrea Giammanco - January 9, 2009

Why not the laude?

3. Luboš Motl - January 9, 2009

Dear Tommaso, I assumed that your word “he” meant “she” and it was a typo caused by your being a sexist pig. In fact you’re such a sexist pig that I assume that you confuse the sexes even after you reiterated it! 🙂

For a gravity waves person with their lousy low energy, she seems to be pretty good in high-energy physics.

4. dorigo - January 9, 2009

Lubos, I am such a sexist pig that, were you to come here, I’d show you I could treat you like a girl, with proper LubE hahr hahr

Cheers,
T.

5. dorigo - January 9, 2009

Andrea, he slightly messed up a few things, although after some hints he got everything right. For me, the laude can only be given by somebody who shows he or she has understood the matter better than what is required by the course itself.

6. Mauro Da Lio - January 9, 2009

And here is another exam:

“Determine the step response of a 1 degree of freedom linear damped oscillator”.

After a long and wandering elaboration, the student ended with a formula written in a horrible calligraphy.
He got 15/30 (insufficient). He asked why and he was told the reason was that he only did the computations but failed to graph the step response and explain it.

The student complained that “it was not asked to explain the results”.

He got 15!

dorigo - January 10, 2009

Hmmm Mauro, I am unable to judge whether you’ve been fair with the student. And a good calligraphy is nice, but who cares about it these days ? OTOH I know that correcting a bunch of tests badly written takes three times longer, so it is mostly a matter of good education.

Cheers,
T.

7. cormac - January 9, 2009

The student, Tommaso? You mean there is only one in the class?

dorigo - January 10, 2009

Nope, I meant I gave the exam to one student only.

Cheers,
T.

8. Luboš Motl - January 10, 2009

Hi Tommaso, I would almost certainly enjoy being treating like a girl – well, in most contexts. 😉

Unfortunately, my hair patterns and overall figures slowly converge to reveal more maleness and less femaleness these days!

The similarity with your daughter was about the eyes, nose etc., anyway.

9. carlbrannen - January 12, 2009

For me, a substantial part of my college education was learning that life isn’t fair, has never been fair, is never going to be fair, and isn’t meant to be fair. Nevertheless, I think it would be nice to only grade students on the work they were asked to do, and not to mark them down 15/30 because they’re not sufficiently psychic.

10. philip - January 13, 2009

Somebody shut Lubos up.

11. Philip - January 14, 2009

Or, according to Lubos’ way of speaking, “Somebody shut the Lubos up. And that’s the memo.” 😉

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