Binding energy between nucleons vs BE inside nucleons

[alexbib]

humm, I've been wondering:

the mass of a nucleus is less than the sum of the masses of the constituent nucleons because of the binding energy. This is how we can get energy out of fusion and fission events.

on the other hand, the mass of a proton or a neutron is MORE than the sum of the masses of the constituent quarks.

Afaik, both the binding of a nucleus and the binding of a proton are consequences of the strong force, so how come one type of binding increases the mass while the other type decreases it?

Thanks.

 

[alexbib]

come on, nobody knows?

 

[marlon]

Well the case of the nucleus mass being smaller then the constituent nuclei is indeed due to the negative binding energy. This is shown by the semi-empirical mass formula. The nucleon-nucleon potential becomes repulsive at very short distances.

Now, let us look inside a nucleon :

The sum of the constituent quarkmasses is much smaller then the mass of the hadron. The extra mass comes from the potential and kinetic energy of the quarks and also from dynamical quarks.

For example the proton contains three valence quarks of three different colours (red, green and blue), but it also contains dynamical (sea) quarks. These are quark-antiquark pairs that appear and disappear through energy fluctuations in the vacuum.

These dynamical quarkpairs will generate mass. The mass of a hadron is bigger then the sum of the masses of the constituent quarks (the three quarks of the proton). But the dynamical quarks also generate mass (via symmetry breaking) , so in the end the mass of a proton is BIGGER then the sum of the three quark masses.

Keep in mind that the three quarks are confined, yielding a rise in their linear potential (dominant in the long range). Once a certain distance is exceeded there is enough energy to create a quark antiquark pair


marlon

 

[marlon]

ps check out the link in the latest entry of my journal

marlon

https://www.physicsforums.com/journal.php?s=&journalid=13790&action=view

 

[alexbib]

Alright, it does indeed make sense.
Thanks a lot!