Why Do Hadrons Weigh More Than the Sum of Their Quarks?

[roberto85]

why is it that a composite particle such as a hadron have a mass which is more than the combined rest mass of it's components? For example the proton has mass 938.27... MeV/c^2 whereas the quarks have masses only totalling approximately 8-12MeV/c^2?

I assume there is a formula used to calculate the combined mass of these particles, if so could someone please let me know it? Id like to be able to use it to be able to calculate masses of mesons and baryons from their quark components. Many thnaks

 

[the_house]

why is it that a composite particle such as a hadron have a mass which is more than the combined rest mass of it's components? For example the proton has mass 938.27... MeV/c^2 whereas the quarks have masses only totalling approximately 8-12MeV/c^2?

The extra mass comes from the energy present in the hadron (recall E=m c^2). It's a relativistic, highly energetic system.

I assume there is a formula used to calculate the combined mass of these particles, if so could someone please let me know it? Id like to be able to use it to be able to calculate masses of mesons and baryons from their quark components.

Sounds great. I'd like that too! Unfortunately, our tools for calculating things non-perturbatively in QCD are extremely limited, and the masses of hadrons are not quantities that can be calculated in perturbation theory. The only method that I know of that can be used for such a thing is http://en.wikipedia.org/wiki/Lattice_QCD" , which is extremely computationally expensive, but has already been used successfully to calculate the mass of, e.g., a proton. There's definitely no simple analytic formula, as nice as that would be.

 

[roberto85]

oh yes lattice qcd. another question is how many gluons are in a proton?

The extra mass comes from the energy present in the hadron (recall E=m c^2). It's a relativistic, highly energetic system.




Sounds great. I'd like that too! Unfortunately, our tools for calculating things non-perturbatively in QCD are extremely limited, and the masses of hadrons are not quantities that can be calculated in perturbation theory. The only method that I know of that can be used for such a thing is http://en.wikipedia.org/wiki/Lattice_QCD" , which is extremely computationally expensive, but has already been used successfully to calculate the mass of, e.g., a proton. There's definitely no simple analytic formula, as nice as that would be.

 

[the_house]

oh yes lattice qcd. another question is how many gluons are in a proton?

A proton does not have a definite number of gluons.