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May12-04, 07:16 AM
humanino's Avatar
P: 2,828
Maybe the problem is how to assign mass to quarks. There are different definitions for what you call mass in the case of quarks, and one must be careful not to speak too loosely about it. Notice that leptons have a very well defined mass, even though it might not be precisely measured (yet).

One definition is the coefficient that appears in the Dirac part of the QCD lagrangian. This results in a renormalized mass, or "running mass", which is usually what one considers as the true mass for the quarks, and is called Standard Model mass.

An other one is furnished by the quark model. This is a classical interpretation, as :
Mass(composite object) = Sum[ Mass(constituents) ] + Binding_Energy (which is negative !)
In my opinion, this is closer to what one determines in String theory. But this is doubtlessly flawed by the fact that the term Binding_Energy is meaningless here, at least on a classical level, because of confinement.

There are still other definitions. In lattice QCD, the mass of the quarks are "bare mass", different from the running MS mass. These parameters are to be determined, so as to produce optimized numerical value for known quantities, such as meson mass.

So, as a conclusion : do not expect anyone to give you a true value for the quark mass, unless first providing a correct definition for this quantity