Neues vom Nordkap

30.08.2004 08:16

The first exam is over. There is not that much to say about it, it's just over. But afterwards I allways ask myself why I've been so nervous. Anyway I had a nice weekend off and finally found my "dejeuner en fourrure" of Meret Oppenheim at the MoMA. The last time I was there, the last time I had guests from Switzerland, I missed it.
Thanks to Martin for figuring out this decay. It is a double weak decay.
|s> --W---> |u>
|u> --W+--> |d>
The W- and the W+ combine to form the Pi0. But I still don't know why this decay is so dominant (it is over 99% of all Xi0 decays) over the following:
|ssu> --W---> |uus> = Sigma+
with only one W exchange. The mass differences aren't that big.

24.08.2004 14:56

When I post physics problems here, it is just to get rid of them. Because when I reread them after a certain time, I normally must admit that they resulted by a misunderstanding of mine. So I hope this will again be the case. I apologize for boring those of my readers who don't care about details of particle physics. I know, I only state these problems here without explanation. So it is quite impossible to understand for non-physicists. That's worse for me though, since you can't help me with some nice hints. Ok, then:
How does the following decay take place?
Xi0 = |ssu> -> Lambda = |uds> + Pi0 = |uuBar> + |ddBar>
It must be a weak charged current as far as I know these are the only flavour changing decays. But there is nothing charged about it. The initial and the final state particles are all neutral. Nevertheless it is the dominant decay for the Xi0, (see the Particle Data Group page.)

17.08.2004 20:55

Good the Olympics are on their way, so people might forget about this ridiculous Rechtschreibereform. It's a shame, but it made its way through to Preposterous. Anyway most people probabely think we are most happy here in Germany since we have time to complain about the bad influence of "Schifffahrt" on our kids.

17.08.2004 20:36

The answer to question two is quite simple:

It turned out that the wavefunction corresponding to Spin * Space * Flavour of a Baryon is symmetric under exchange of any two quarks. That was the reason why the coulour quantum number was postulated in the first place. Let's write the wavefunction of a Baryon as a product
psi = J(Spin) * S(pace) * F(lavour) * C(oulour)
Now consider a Baryon consisting of three quarks of the same flavour, say the Delta++.The F function must be symmetric otherwise it vanishes.So J and S have to be both antisymmetric or both symmetric. if they are both antisymmetric the S part can't be build by a product of three groundstate wavefunctions since that again would vanish. So the lightest possible Baryon with identical quark content is the one with symmetric S and J (and F) you expect all of the quarks to have an s-wavefunction and therefore they must have parallel Spins J = 3/2.

16.08.2004 14:49

Some more questions on particle physics:

11.08.2004 07:22

Some things I would do if there weren't these exams:

09.08.2004 08:41

04.08.2004 08:49

Schau an, da gibt es nicht weit von meiner Heimat eine Magdalena Einsiedelei und ich wusste nix davon. Das ist ja mal ein Spaziergang ins Freiburgische wert.

03.08.2004 14:08

Wenn nun auch Frau Buhlmans Verbot von Studiengebühren fällt, und die unionsregierten Länder Gebühren einführen, die SPD regierten hingegen nicht, dann könnte das tatsächlich zu einem zwei Klassensystem führen. Denn die Studenten, die die Gebühren nicht zahlen wollen, oder nicht zahlen können und keinen Kredit aufnehmen wollen, werden in SPD Lande umsiedeln und diejenigen, die reich genug sind oder aber für eine bessere Ausstattung und eine bessere Betreuung (was hoffentlich ein sekundär Effekt von Gebühren = mehr Geld, und studentischer Abwanderung = besseres Verhältnis von Lehrenden zu Studenten, ist) bereit sind, sich zu verschulden, werden in CDU Lande ziehen.

02.08.2004 09:24

Well, I am still surfing the web instead of studying. There is a nice post of Chad Orzel on a phycisists every day life.

02.08.2004 08:59

Chemical elements, biological species and mountains are often called after their discoverer or the place where the have been found. (At least the ones you don't encounter in an normal Western everyday life.) Particles aren't, with two exceptions: the J of the J/psi and the Higgs. But Mr. Ting at least conformed with the naming standard of the particle community, reducing his name to a letter. (J is similar to the Chinese sign for Ting). So there remains the Higgs. (I don't now who called it "Higgs", most probabely it wasn't Peter Higgs himself).
But maybe there is no Higgs at all, that would save the matter.


About me

My name is Magdalena Luz. I am a physicist, now working as a software engineer in Zürich, Switzerland.




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