The claim is often made that the discovery of the Higgs boson will give us information about the origin of mass. However, the bare masses of the up and down quarks are only around 5 MeV, quite a bit smaller than their "constituent" or "dynamical" mass of around 300 MeV. (Remember that a neutron, for example, is one up and two down quarks and has a total mass of 939 MeV.) What then, is the reasoning behind the claim that the Higgs will address the origin of mass when by far the majority of the mass of the neutron (and proton) is related instead to the dynamical breaking of chiral symmetry?
[Physics] The contribution to mass from the dynamical breaking of chiral symmetry
higgsmassparticle-physicsquantum-chromodynamics
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You are understanding correctly. In the massless up/down quark limit, chiral symmetry is restored, and the pion becomes massless but quarks are still confined, and baryons have about the same mass as they do now. This is exactly why the idea that the pion is made of quarks is nonsense.
In the 1980s, many in the new generation sought to undo the progress of the 1960s, and willfully ignored the revolutionary work of Nambu, Sakurai, Skyrme, and others, dismissing it as pre-quark nonsense. They decided that a pion is made up of two nonrelativistic quark-objects, they called these objects "constituent quarks", and they made up force laws for these to reproduce the Hadron spectrum. Georgi and Glashow even went so far as to invent a quark-quark coupling force which was designed to lower the mass of the pion by interquark interactions!
This work is a little embarassing to read. The proper model of the pion was the much earlier one due to Nambu and Weinberg, and this is now verified thanks to numerical lattice QCD, where the mass of the quark can be tuned at will. When you tune the mass of the quarks to zero, the pion mass vanishes according to the laws of chiral peturbation theory.
The pion is a mode of oscillation of the quark chiral condensate, a material filling all of space. It is made out of quarks which are created by the independent fluctuations of the gluon field.
The gluon field completely randomizes on a Baryon scale, meaning that a quark going in a closed path larger than a proton circumference will get a completely random pick from SU(3) as its holonomy. A random gauge field will create large numbers of objects whose mass scale is much lower than this randomization scale, and in this case, the objects it creates are the light up and down quarks, and to a lesser extend strange quarks. These quarks condense in pairs in the vacuum, making a condensate whose order parameter is much like a mass term in the Dirac equation: $m \bar\psi \psi$. This condensate is not invariant under rotations of the left and right-handed quarks into each other, but the Lagrangian is (more or less, except for the negligible quark mass).
The Goldstone modes of the broken symmetry are waves in this condensate, and these are the pions. The goldstone mode is due to oscillations where the left and right part of the condensate slosh in phase in opposite directions, and these are collective excitations of quarks. The pion is made of quarks to the same extent that a sound wave is made of atoms.
That the pions are Goldstone bosons was not only theoretically predicted by Nambu, it explains their strange derivative couplings at low energy, and this was spectacularly extended to a full theory by Weinberg's soft-pion theorems, and chiral perturbation theory. The condensates were further used to give nonperturbative corrections to QCD particle propagation at intermediate distances in the Shifman-Vainshtein-Zakharov sum rules. So really, everyone should have known better than constituent quarks.
It is not clear that the notion of "constituent quark" actually has any form of real meaning, or whether it is just a figment of the imagination. The only partial evidence in it's favor that I think is not easy to explain in other way is that the total cross sections for pions are about 2/3 the total cross section for protons, as if the pomeron hits 2 quarks instead of three. I don't know if this approximate equality is not just a coincidence.
You have drawn a Feynman diagram.
Feynman diagrams are iconic shorthand for integrals over the variables of the problem. The calculation gives the probability for the reaction to happen, in this case the decay of a neutron .
The observables are the four vectors of the initial (neutron) and final particles. The integral is over the variables .
Here is a simpler labeled diagram
The Feynman diagram for the Coulomb interaction (electric force), along with the parts of the Feynman integral they correspond too. Every part of this is really nasty. For example, that "g" is actually 16 numbers.
This is the expression that has to be integrated over the limits of the variables.
The electric force (what physicists call the “Coulomb force” to look smart) is mediated by photons. That is to say, particles with charge push or pull on each other using photons. The diagram above is the “first order Feynman diagram” for two electrons repelling each other. The probability amplitude of two electrons with momentum p and k pushing off of each other and flying off again with momentum q and l is given by:
If you’re wondering which particles are virtual and which are real: virtual particles are the ones stuck inside the diagram and real particles are the ones going in and coming out (they might go on to be detected somewhere).
The incoming lines represent real particles, and also the outgoing lines. The line in between represents the functions under the integral. This line has to carry the charge and quantum numbers that conservation laws impose. In addition there exists a function under the integral, called a propagator, which has in the denominator the mass of the named particle. In the case above it is the photon's zero mass.
Under the integral the four vector of this "photon" line cannot have zero mass because of the spread of the variables of integration, so it is off mass shell and called a virtual photon.
In your diagram for neutron decay the corresponding denominator is ((p-q)^2-m_W^2). The large mass is crucial and represents together with the coupling constant, the "weakness" of the interaction. That is why the internal line is identified with the W. It has all the quantum numbers but a variable mass of the four vector it represents. It is called virtual for this reason.
The W boson mass comes within the integral represented by the diagram, in the denominator of the propagator. The line represents an off mass shell virtual W.
Best Answer
The extra mass of the proton and neutron is not due to chiral symmetry breaking. It is due to the energy in the electromagnetic and strong force fields.
If chiral symmetry were an exact symmetry of the Lagrangian then the pions and other mesons (not the baryons) would have zero mass due to spontaneous chiral symmetry breaking. The chiral symmetry is not exact due to the small bare masses of the quarks so the mesons are not exactly massless.
From this you can see that your question is a bit confused, but one part that is correct is that most of the mass in ordinary atomic matter is not due to the Higgs mechanism. When people say that the Higgs boson will give us information abut the origin of mass they mean the bare masses of non-composite particles such as electrons and quarks.