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Nov26-03, 03:30 PM
P: 209
Originally posted by turin
Does understanding of this stuff rely on an understanding of QFT? How (what method do you recommend) does one learn QFT: class at university, book, internet ...?
Yeah, a knowledge of quantum flavor dynamics is the basis for dealing with these things in general. Classes are good, but personally I enjoy reading books on my own much better. I would actually reccommend a book called Introduction to Quarks and Partons; it was published in the early 1980's, so its a bit of a throwback to the days when charmonium physics had just arrived on the scene. It does an excellent job of laying out the transformations and mixing for SU(3) flavor states of hadron multiplets. SU(3) only takes into account the three lightest quarks, so the mixing between the states is prevalent, whereas the heavier quarks beyond SU(3) hardly mix at all.

Originally posted by turin
Why do you say "... in an intense electromagnetic field ...?" Is this a catalyst or a requirement or what?

I don't have it clear why charged particles emit photons (what motivates the emition, symmetry or something?)
This is defined as Bremstrahlung. Look up the process on the internet or in a text.

Photons naturally couple to and from charged particles via the electromagnetic term of the electro-weak Lagrangian;


where Q is the electric charge (in units of the positron charge), A is the massless photon field, and e is the coupling (equal to the positron charge, related to the natural coupling g by the Weinberg angle).

Originally posted by turin
OK, so the strong potential goes as x2, like the quarks are connected by rubberbands or something? Then, around each baryon, is there a "meson cloud" that can couple to the "meson cloud" of another baryon? It still just seems that the one baryon's business is it's own. I don't see where the other baryon comes in. Does another baryon come up with a "knife" and cut the meson loose, thus lowering the energy of the other baryon that had the stray meson?
Yes, that is a fairly good approximation. Just remember that due to wave-functions and such, no baryon (or meson, or anything for that matter) can be treated as a totally isolated system. Just like electrons do not need to collide in order to interact, baryons do not need to collide to interact, either.

A baryon does not contain additional mesons; rather it emits mesons on a regular basis, some real and some virtual, from the "sea" of quarks and antiquarks. A baryon does not simply come up to another baryon and collide with it to "cut off" a meson. The meson is emitted, not removed forcibly. Through the interaction of the baryons with the emitted mesons, baryons can be confined within nuclear bonds. The Yukawa hypothesis identified mesons, in particular the pion, as the force carrying particles that enabled protons and neutrons to be confined in the nucleus of an atom

Now, collisions of baryons do occur in the lab, and they are excellent tools for probing the constituents of baryons (as in the pp collision Drell-Yan process, elastic scattering scaling behaviors, etc.).