Naked Science Forum

Non Life Sciences => Physics, Astronomy & Cosmology => Topic started by: jeffreyH on 04/12/2017 12:58:27

Title: Have the quark masses been determined?
Post by: jeffreyH on 04/12/2017 12:58:27

I found the following which appears to say that the quark masses have been determined to a high degree of accuracy. Is this still the case?
https://m.phys.org/news/2010-05-masses-common-quarks-revealed.html

Title: Re: Have the quark masses been determined?
Post by: evan_au on 04/12/2017 20:44:32

One part of the problem is separating the quarks from each other - you can't do it without creating more particles.
- Another part of the problem is separating the mass of the quark from the mass of the surrounding gluons.
- Perhaps why the author of that paper set out to calculate the masses on a supercomputer?

Quote from: Wikipedia

a proton has a mass of approximately 938 MeV/c², of which the rest mass of its three valence quarks only contributes about 9 MeV/c²; much of the remainder can be attributed to the field energy of the gluons.

See: https://en.wikipedia.org/wiki/Quark#Mass

Title: Re: Have the quark masses been determined?
Post by: jeffreyH on 04/12/2017 23:08:32

I've been looking at hydrogen atom and molecule ionizing energies. They are in electron volts rather than mega electron volts. So orders of magnitude less than nucleon separation energies. Nothing seems to mesh together. You can forget symmetry. There has to be some order in there somewhere.

Title: Re: Have the quark masses been determined?
Post by: evan_au on 05/12/2017 10:25:38

Quote from: JeffreyH

I've been looking at hydrogen atom and molecule ionizing energies. They are in electron volts rather than mega electron volts. So orders of magnitude less than nucleon separation energies. Nothing seems to mesh together.

How about looking at it just using classical electrostatic forces:
- Consider the energy to separate an electron and a proton to infinity, if you consider them as point charges, at an initial separation of 120pm (the radius of a Hydrogen atom). It ends up a little over 10eV.
- Now consider the energy to move together two protons from infinity, if you consider them as point charges, at final separation of 1.6fm (the diameter of a proton). It ends up in MeV.
- If a Helium nucleus is to be stable, the nuclear force must be strong enough to overcome this electrostatic repulsion.

The magnitude of the charge is not any different in the two cases, but the separations differ by orders of magnitude... plus the inverse square law makes the difference even more dramatic!

Title: Re: Have the quark masses been determined?
Post by: jeffreyH on 05/12/2017 12:58:59

To get a fuller picture the coulomb barrier needs to be incorporated. Hence why I am only interested in hydrogen isotopes at the moment.
https://en.m.wikipedia.org/wiki/Coulomb_barrier