# Parton Distributions in PP collisions

by philip041
Tags: collisions, distributions, parton
 P: 107 I read some notes answering a question about how a Z boson is made in a proton anti-proton collision and it said that the quark antiquark collision is a very rare event because the antiquark has a small parton distribution function. Surely the up anti up(or down antidown) parton distributions are the same? The general context is the discovery of the W+ W- and Z bosons. Were these all quite difficult processes to observe? Cheers
P: 2,824
 Quote by philip041 Surely the up anti up(or down antidown) parton distributions are the same?
I can see why their integrals should cancel, but I doubt they must be equal in all variables one can cook.

On top of that, for up or down you have contributions from the sea and the valence as well. The valence is defined as this part which does not cancel when integrated. Depending on your kinematics, the valence may contribute a lot.
 Sci Advisor P: 1,233 Neither the integrals nor the distributions of ubar and dbar are equal. The "Gottfried sum rule" which assumes they are equal has been shown to be violated in several experiments. A good reason for their difference is that there are more pi+ mesons than there are pi- in the proton pion cloud. Use "surely" carefully.
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## Parton Distributions in PP collisions

 Quote by clem Neither the integrals nor the distributions of ubar and dbar are equal.
It was about the equality of u_sea with ubar_sea (on one hand, and on the other hand d_sea with dbar_sea) if I understand the question.
 P: 107 Lol I'm out my depth already, cheers for the replies but I think I will have to hunt my elusive lecturer down...
Mentor
P: 14,656
 Quote by humanino It was about the equality of u_sea with ubar_sea (on one hand, and on the other hand d_sea with dbar_sea) if I understand the question.
Those aren't equal either, I'm afraid.
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 Quote by Vanadium 50 Those aren't equal either, I'm afraid.
That's what I tried to convey in #2
 P: 985 Can you give us the specific quote? I think there may be some misunderstanding here. It is an obvious consequence of CPT theorem that the spin-averaged pdf of the up-quark in proton is equal to the spin-averaged pdf of the antiup-quark in antiproton. And neither of them is small. This quote "the quark antiquark collision is a very rare event because the antiquark has a small parton distribution function" might make sense in the context of trying to observe Z on a proton-proton collider. It is indeed rather unlikely to find an energetic antiquark inside a proton.
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 Quote by hamster143 ...
If I CPT an up quark, I get an antiup, not a down.
 P: 985 grr yes that's what I meant.

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