
#1
Nov912, 09:11 AM

P: 361

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? 



#2
Nov912, 09:39 AM

Mentor
P: 10,853

For the topquark, you can use the invariant mass of W + bjet, as it decays before it forms hadrons.
The masses of charm and bottommesons 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
Nov1112, 02:58 PM

P: 361





#4
Nov1112, 04:05 PM

Mentor
P: 10,853

Hadron component mass
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
Nov1212, 01:10 AM

Sci Advisor
P: 5,307

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 Zmasses; 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
Nov1212, 10:20 AM

P: 361

Photons are massless, yet electrons are not confined in atoms.




#7
Nov1212, 10:46 AM

Mentor
P: 10,853

Photons have no selfinteraction, and the electromagnetic interaction is weak.




#8
Nov1212, 11:00 AM

P: 361

Precisely how does the force of strong interaction (gluon chain) depend on distance for large distances?




#9
Nov1212, 05:31 PM

Sci Advisor
P: 5,307

If you like I can post the exact expression just to convince you that it's not an ordinary potential ;) 



#10
Nov1312, 04:37 AM

P: 361

The more interesting analysis is that of a barrier against tunnel creation of a quarkantiquark 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
Nov1312, 07:54 AM

Mentor
P: 10,853

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 quarkantiquark pair is enough, with an energy of ~2 times the quark masses (~2*5 MeV).



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