What is the Contribution of Heavy Quarks to Proton Structure?

In summary, the Parton Distribution Functions of all parton species yield a total momentum fraction of 1.
  • #1
ChrisVer
Gold Member
3,378
464
I am looking at the structure of protons, and in my script, when they define the Parton Distribution Functions of all parton species they say that the integral over PDFs of all parton species yields a total momentum fraction of:

[itex] \sum_i \int_{0}^{1} f_{i}(x) x dx =1 [/itex]
where [itex]i[/itex] denots the species:
[itex]g,u,d,s,c,\bar{u},\bar{d},\bar{s},\bar{c}[/itex]
Then it says that b or t quarks are not included due to their high mass...
However isn't the [itex]c[/itex] quark pretty massive (1.29GeV >1 GeV) for the proton (~1 GeV)?
 
Physics news on Phys.org
  • #3
They are off-shell quarks, so they don't have to have their on-shell masses. Also those masses are defined in a tricky way since you cannot actually isolate a quark to measure its mass.
 
  • #4
kurros said:
They are off-shell quarks, so they don't have to have their on-shell masses. Also those masses are defined in a tricky way since you cannot actually isolate a quark to measure its mass.

that works fine for me... but if I accept the existence of off-shell quarks, wouldn't the same reasoning work for b or t quarks?
 
  • #5
ChrisVer said:
that works fine for me... but if I accept the existence of off-shell quarks, wouldn't the same reasoning work for b or t quarks?

Yep, pretty sure. Theoretically virtual b and t quarks contribute, but I think they are just negligible so people ignore them.
 
  • #6
There are 5 flavor PDFs. There are not 6 flavor ones because the top contributions are unmeasurably small.
 
  • #7
The b contribution is there (you can measure it via single-top production in proton/proton collisions), but its contribution to the total momentum is quite small. The charm contribution is a bit larger. If you include those two (or just 1) depends on the precision you want. Including the top is pointless because its contribution is tiny compared to the uncertainties from the light quarks.
 
  • #8
Note that the Parton distributions functions are required to describe the evolution of patrons before an interaction.

The point is that quark content arises due to the evolution of patrons. So, by evolving the patrons to high virtuality (q^2), the c, b, or t quarks can effectively contribute to an interaction.

At a 100tev hadron collider, the t quark distribution will have to be studied theoretically and experimentally.
 
  • #9
The b-contribution is also there in four-flavor PDF's. There it comes from the gluon splitting to bbar.

There is no physical distinction between starting with u, d and g PDFs and letting them evolve and starting with 4 or 5 flavor PDFs. It's a question of ease of calculation and ease of comparison with data.
 
  • #10
The b contribution in the 4 flavour scheme is present in the gluon splitting *only in the matrix element*.

It is neglected from the PDF to allow the b quarks to be treated as massive quarks in the matrix element. This improves the accuracy of the prediction for the b quark in the final state... At a consequence of losing the resummation of b quark contributions in the PDF which are ignored.

The treatment is only the same if you can calculate the full interaction (all orders in the matrix element), which is not and will not be possible.
 

1. What are sea-valance quarks of protons?

Sea-valance quarks are subatomic particles that make up protons, which are part of the nucleus of an atom. They are called "sea" quarks because they are constantly popping in and out of existence in the proton's internal structure.

2. How are sea-valance quarks different from valance quarks?

Valance quarks are the three primary quarks that make up a proton: up, up, and down. Sea-valance quarks, on the other hand, are additional quarks that appear and disappear within the proton's internal structure, providing a more complex picture of its composition.

3. What is the purpose of studying sea-valance quarks?

Studying sea-valance quarks helps scientists better understand the inner workings of protons and how they contribute to the overall structure of atoms. This research can also provide insight into the fundamental forces of the universe and help us understand the origins of matter.

4. How do scientists study sea-valance quarks?

Scientists study sea-valance quarks through high-energy particle accelerators, such as the Large Hadron Collider, which can break down protons and allow researchers to observe the interactions of individual quarks. They also use mathematical models and simulations to study the behavior of these particles.

5. Are sea-valance quarks important in other areas of science?

Yes, sea-valance quarks are important in other areas of science, such as nuclear physics and particle physics. They also play a role in understanding the structure and behavior of other subatomic particles, such as neutrons and mesons. Additionally, studying sea-valance quarks can have applications in technology and energy research.

Similar threads

  • High Energy, Nuclear, Particle Physics
2
Replies
46
Views
3K
  • High Energy, Nuclear, Particle Physics
Replies
1
Views
1K
  • High Energy, Nuclear, Particle Physics
Replies
3
Views
1K
  • Advanced Physics Homework Help
Replies
1
Views
722
  • High Energy, Nuclear, Particle Physics
Replies
4
Views
1K
  • High Energy, Nuclear, Particle Physics
Replies
2
Views
885
  • High Energy, Nuclear, Particle Physics
Replies
32
Views
5K
  • High Energy, Nuclear, Particle Physics
Replies
6
Views
2K
  • High Energy, Nuclear, Particle Physics
Replies
5
Views
5K
  • Advanced Physics Homework Help
Replies
1
Views
1K
Back
Top