Exploring the Inertial and Rest Mass of Quarks and Gluons in Hadrons

In summary, the conversation discussed the structure of hadrons and the properties of quarks and gluons. It also explored methods for measuring the inertial mass of quarks and how gluons are proven to be massless. The theoretical and experimental implications of massive gluons were also discussed, with a focus on the strong interaction and its dependence on distance. The conversation concluded with a discussion on the classical picture of gluon chains and the energy gain involved in snapping them. Overall, the conversation highlighted the complexities of the quantum mechanical nature of the strong force and the challenges in understanding it.
  • #1
snorkack
2,186
472
Quarks are imprisoned in hadrons, and have large binding and kinetic energies at all times. Ditto about gluons.

How can inertial mass of quarks inside hadrons be measured?

Also, how is it proven that gluons are massless? What effects would happen if gluons had rest mass, as much as up to a few MeV?
 
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  • #2
For the top-quark, you can use the invariant mass of W + b-jet, as it decays before it forms hadrons.
The masses of charm- and bottom-mesons are dominated by the heavy quark, too.

For other quark masses: Compare theory predictions (based on the quark masses) with experimental results and use the comparison as indirect measurement of the masses.

I think massive gluons would give serious theoretic problems.
 
  • #3
mfb said:
I think massive gluons would give serious theoretic problems.

So can someone explain just which the theoretical results are?
 
  • #4
Quantum field theory uses fundamental symmetries to construct interactions between particles. To have those symmetries, bosons have to be massless.
The masses of W and Z bosons (weak interaction) were a serious issue, until Higgs and some other theoreticians developed the Higgs mechanism - it breaks the symmetry and adds mass to those bosons.
If you want to add masses to gluons, too, you need something similar for the strong interaction.

Oh, and then there are experimental limits: 1 2
 
  • #5
With massive gluons there would be no confinement! There is no confinement due to the el.-weak force which differes from QCD in i) an additional U(1), ii) SU(2) instead of SU(3) and iii) W- and Z-masses; i) is irrelevant for confinement, ii) yields a confining theory as we know from lattice calculations, iii) is the major difference and spoils confinement
 
  • #6
Photons are massless, yet electrons are not confined in atoms.
 
  • #7
Photons have no self-interaction, and the electromagnetic interaction is weak.
 
  • #8
Precisely how does the force of strong interaction (gluon chain) depend on distance for large distances?
 
  • #9
snorkack said:
Precisely how does the force of strong interaction (gluon chain) depend on distance for large distances?
It's not possible to write down a "classical potential" for the strong interaction mediated by gluons. The expression which can be derived is viable only as a non-local operator acting on a Hilbert space. One can extract something like a "potential" between "static valence quarks" mediated by gluons which has V(x) ~ x asymptotics for large x, but this is not a fundamemtal expression.

If you like I can post the exact expression just to convince you that it's not an ordinary potential ;-)
 
  • #10
The more interesting analysis is that of a barrier against tunnel creation of a quark-antiquark pair, cutting the gluon chain.

If a hadron contains at least two up or down quarks then the lowest barrier path to snap the gluon chain is pion creation, with 140 MeV energy.

Of course, after snapping the chain, the halves are STILL stretched... where does the energy gain driving the gluon chain snapping come from?
 
  • #11
That is a very classical picture, and its application is limited - the system is quantum mechanical. To "cut the chain", you do not have to create a bound hadron state (pion). A quark-antiquark pair is enough, with an energy of ~2 times the quark masses (~2*5 MeV).
 

1. What are quarks and gluons?

Quarks and gluons are subatomic particles that are the building blocks of protons and neutrons, which make up the nucleus of an atom. Quarks have a fractional electric charge and interact through the strong nuclear force mediated by gluons.

2. What is the inertial mass of quarks and gluons?

The inertial mass of a particle is a measure of its resistance to acceleration and is related to the amount of energy required to accelerate the particle. The exact value of the inertial mass of quarks and gluons is not known, but it is believed to be very small due to their high speeds and interactions with the strong force.

3. How is the rest mass of quarks and gluons measured?

The rest mass of a particle is its mass when it is not moving. In the case of quarks and gluons, their rest mass cannot be measured directly because they are always confined within hadrons. Instead, scientists use mathematical models and experimental data from particle collisions to estimate their rest mass.

4. Why is exploring the inertial and rest mass of quarks and gluons important?

Understanding the properties of quarks and gluons is crucial for understanding the fundamental laws of nature and the behavior of matter at the subatomic level. This knowledge can also help us develop new technologies and advance our understanding of the universe.

5. How do scientists study the inertial and rest mass of quarks and gluons in hadrons?

Scientists use a variety of methods, including particle accelerators, to study the interactions between quarks and gluons and to measure their properties. They also use theoretical models and computer simulations to make predictions and test their understanding of these particles.

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