Feynman Diagram

  • #1

Homework Statement


Draw the Feynman diagram for:
e[tex]^{-}[/tex] + p [tex]\rightarrow[/tex] n + [tex]\upsilon[/tex][tex]_{e}[/tex]

Sorry, I dunno how to make everything even but you should get the gist.

Homework Equations





The Attempt at a Solution



Well, what I have is the electron and proton annihilating(and this is what confuses me) into a Z[tex]^{o}[/tex] which in turn becomes the neutron and electron neutrino. Is this correct?
 

Answers and Replies

  • #2
malawi_glenn
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no that is incorrect, protons and neutrons are not elementary particles.

Hints:
Think of their quark content, is there something going on there? What differs in quark content from proton and neutron?
 
  • #3
Ah, duh! Thanks for the hint!
 
  • #4
turin
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I'm going to be picky and disagree. What is so wrong with having a W-p-n vertex (a charge current in which a proton couples to a W by converting to a neutron)? The other quarks are just spectators anyway.
 
  • #5
malawi_glenn
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I'm going to be picky and disagree. What is so wrong with having a W-p-n vertex (a charge current in which a proton couples to a W by converting to a neutron)? The other quarks are just spectators anyway.

Because OP thought the interaction was an electron + proton annihilate to virtual Z ....

Your suggestion is also correct, but doing thing on quark level is more accurate.

The most important thing is the exhange mehcnaics altouhg.
 
  • #6
turin
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... but doing thing on quark level is more accurate.
I maintain my disagreement, now even more adamantly. This is a tautological accuracy. The accuracy to which I can predict the statistics of this kind of scattering relies on the accuracy of the up-PDF, which in turn was determined by measuring the statistics of this kind of scattering (among others, I do admit). If we somehow have developed a way to predict the PDFs, then I would agree with you, but, as far as I know ... All I disagree with is the notion that scattering is less accurately described in terms of "composite" particles.
 
  • #7
malawi_glenn
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I would say it is a semantic disagreement.

i) You THOUGH the OP was referring to the process you suggest?

ii) Of course one can ignore quark structure, I only suggested that he should look at the protons and neutrons quark structure to verify that his suggested solution that the proton and electron annihilate to form virtual Z is impossible. I NEVER said that he had to draw feynman diagram on the quark level.
 
  • #8
turin
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I guess you're right. For the benefit of alex and others (including myself), perhaps you would like to continue the discussion:

I was ruling out the Z production based on conservation of lepton and/or baryon number. Neither one of these numbers cares about compositeness of the proton, and the argument based on either one of these conservations works for a composite proton just as well as an elementary proton.

You were ruling out the Z production based on conservation of charge and/or color. Both of these numbers rely on the compositeness of the proton, and the argument based on either one of these conservations does not work unless one realizes, as you pointed out, that the proton is composed of quarks with color and fractional charge.

In particular, if we learn that the quark model and the SU(3) color symmetry are wrong, then your argument would cease to be valid, but the proton would remain stable. Conservation of baryon number should hold, for whatever reason, or else the proton would decay, I think.
 

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