Gluon Mass: What Causes 50% of Nucleon Mass?

[wolfgang]

Hi,

We know that the gluons rest mass is 0.On the other hand we also know that the u and d quarks that compose the nucleons are responsible for the 50% of the nycleons mass for the rest 50% are responsible the gluons!

Why the massless gluons “gain” mass when they are inside the nycleons?

Thanks for your time.

 

[wolverine]

They do not gain mass ...

It is the interaction of the gluons (with themselves by strong interaction cos' they get color, with the quarks ..) that give the major part of the mass of the nucleon

(think of the famous E = m * c * c, that bond mass to energy);

 

[vanesch]

On the other hand we also know that the u and d quarks that compose the nucleons are responsible for the 50% of the nycleons mass for the rest 50% are responsible the gluons!

Maybe I should add a small "correction" to this statement. What has been found by deep-inelastic experiments, is that at high energies, about 50% of the momentum of a proton must be carried off by non-electromagnetically interacting particles, and the obvious candidates are gluons.
The way this is inferred is that at high energies, deep inelastic electron-proton collisions allow to determine the "population" of quarks as a function of a dimensionless parameter x-Bjorken, which is nothing else but the fraction of the total proton momentum carried by the colliding quark. When integrating this population to find the total momentum carried by "partons interacting with the electron", one arrives at about half the momentum of the proton. Hence the other half has to be carried somehow (within the parton model) by something that is not seen by electrons.
However, it is probably not fair to extrapolate this to the rest mass of a proton, which is more related to the energy levels of bound states in QCD.

cheers,
Patrick.