Parton Distributions in PP collisions

In summary, the conversation was about the difficulty of observing Z bosons and the differences in the parton distribution functions of up and antiup quarks in a proton-antiproton collision. It was mentioned that the integrals and distributions of ubar and dbar are not equal, and that the Gottfried sum rule has been shown to be violated in experiments. The possibility of CPT theorem playing a role in this was also discussed. It was concluded that due to the small parton distribution function of the antiquark, it is rare to find an energetic antiquark inside a proton, making it difficult to observe Z bosons in a proton-proton collision.
  • #1
philip041
107
0
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
 
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  • #2
philip041 said:
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.
 
  • #3
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.
 
  • #4
clem said:
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.
 
  • #5
Lol I'm out my depth already, cheers for the replies but I think I will have to hunt my elusive lecturer down...
 
  • #6
humanino said:
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.
 
  • #7
Vanadium 50 said:
Those aren't equal either, I'm afraid.
That's what I tried to convey in #2
 
  • #8
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.
 
Last edited:
  • #9
hamster143 said:
...
If I CPT an up quark, I get an antiup, not a down.
 
  • #10
grr yes that's what I meant.
 

1. What are parton distributions in PP collisions?

Parton distributions refer to the probability of finding a specific type of parton (quarks and gluons) with a certain momentum fraction inside a proton. PP collisions, also known as proton-proton collisions, are high-energy collisions between two protons that take place in particle accelerators. These collisions can help us study the behavior and properties of partons.

2. Why are parton distributions important in PP collisions?

Parton distributions are important because they provide crucial information about the internal structure of protons. By studying the distribution of partons in PP collisions, we can better understand the fundamental interactions between particles and the strong force that holds them together.

3. How are parton distributions measured in PP collisions?

Parton distributions cannot be directly measured, but they can be inferred through the analysis of data from PP collisions. This data is collected by detectors in particle accelerators and analyzed using theoretical models and statistical methods to determine the probability distributions of partons within protons.

4. What factors can affect parton distributions in PP collisions?

There are several factors that can affect parton distributions in PP collisions, such as the energy and momentum of the colliding protons, the type of collision (e.g. elastic or inelastic), and the kinematics of the final-state particles. The presence of other particles in the collision, such as quarks or gluons from other protons, can also have an impact.

5. How do parton distributions in PP collisions contribute to our understanding of the Standard Model?

The Standard Model is a theoretical framework that describes the fundamental particles and their interactions. Parton distributions in PP collisions provide valuable information about the behavior of quarks and gluons, which are the building blocks of protons and play a key role in the Standard Model. By studying these distributions, we can test and refine our understanding of the fundamental forces and particles in the universe.

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