Quarks in Protons

[csmyth3025]

I just recently became aware of the following:

 

Most of a hadron's mass comes from the gluons that bind the constituent quarks together, rather than from the quarks themselves. While gluons are inherently massless, they possess energy—more specifically, quantum chromodynamics binding energy (QCBE)—and it is this that contributes so greatly to the overall mass of the hadron (see mass in special relativity). For example, a proton has a mass of approximately 938 MeV/c², of which the rest mass of its three valence quarks only contributes about 11 MeV/c²; much of the remainder can be attributed to the gluons' QCBE

(ref. http://en.wikipedia....wiki/Quark#Mass )

 

This new (to me) information certainly blurs the line between what I once thought I could correctly call mass and what I could call energy. I am well aware that these terms are considered by physicists to describe two different aspects of essentially the same thing (E=mc^2). Still, this description of hadrons somehow comes as a surprise to me.

 

So now I have to think of protons and neutrons and, indeed, atomic nuclei as a mixture of nearly 99% binding energy and a little more than 1% "mass". Is this 1% mass irreducible or can it also be converted into an equvalent amount of energy?

 

I must admit that this whole energy<-->mass thing is starting to confuse me.

 

Chris

[IM Egdall]

This is a tricky subject. But I'll try.

 

Per E-mc^2, mass and energy are equivalent. So like mass, energy has weight. And since fields have energy, they have weight too.

 

If you measure the rest-mass of all the fundamental particles in your body (quarks, electrons, gluons, photons), it accounts for only a small amount of your body's weight. When you weigh yourself on your bathroom scale, most of your weight is due to the strong and electromagnetic force fields between the quarks in your body.

 

To quote:

 

. . . 90 (to) 95 percent of the mass of matter as we know it comes from energy. We build it up out of massless gluons, (massless photons), and almost massless quarks, producing mass from pure energy. That's the deeper vision.

 

- Frank Wilczek

 

 

Frank Wilczek, E = mc2 Explained, NOVA Science Programming on Air and Online.

 

 

[csmyth3025]

One of the reasons that I wondered if the mass of quarks, electrons and neutrinos is irreducible has to do with big bang nucleosynthesis. As I understand it, at the end of this very early stage of the universe there was a smattering of matter left over after all of the particle-antiparticle annihilations were done. This smattering is all of the matter in the universe today.

 

Antiparticles can annihilate our matter particles today - but we have to make them artificially. As far as I know, there isn't enough antimatter in the universe to cancel out the matter. Are there other ways to transform massive particles into massless particles (photons)?

 

Chris

 

Edited to correct spelling error.

Edited May 2, 2011 by csmyth3025

[IM Egdall]

One of the reasons that I wondered if the mass of quarks, electrons and neutrinos is irreducible has to do with big bang nucleosynthesis. As I understand it, at the end of this very early stage of the universe there was a smattering of matter left over after all of the particle-antiparticle annihilations were done. This smattering is all of the matter in the universe today.

 

Antiparticles can annihilate our matter particles today - but we have to make them artificially. As far as I know, there isn't enough antimatter in the universe to cancel out the matter. Are there other ways to transform massive particles into massless particles (photons)?

 

Chris

 

Edited to correct spelling error.

 

There are all kinds of particle decays. Heavier fundamental particles are unstable and decay (transform) into lighter particles. But I believe conservation laws do not allow a matter particle (lepton or quark) to decay completely into massless particles (guage bosons) like photons or gluons. See link:

 

http://hyperphysics.phy-astr.gsu.edu/hbase/particles/parint.html