- #1
NLB
- 23
- 0
Does anyone know the magnetic moments of the up and down quarks? I am interested only in the best experimental data, not theoretical estimates.
tom.stoer said:I guess identical for all elementary spin 1/2 particles; why do you expect a difference? QCD corrections?
Do you mean like an electron's magnetic moment? It's not possible to get an up or a down quark into that state, or any other quark into that state, as far as anyone knows. That's quark confinement. It takes too much energy to separate them by more than 10-15 m.NLB said:Does anyone know the magnetic moments of the up and down quarks? I am interested only in the best experimental data, not theoretical estimates.
NLB said:I just recently read that the mass of the three quarks is much smaller than the mass of the proton ... This is why certain theories suggest that there are more quarks in nucleons than just the three valance quarks
lpetrich said:But one can easily estimate these quarks' magnetic moments when bound in nucleons.
... 1/sqrt(18) *
(2|u+u+d-> - |u+u-d+> - |u-u+d+> + 2|d-u+u+> - |d+u+u-> - |d+u-u+> + 2|u+d-u+> - |u-d+u+> - |u+d+u->)
One can easily find the magnetic moment:
muu/qu = 2.78
mud/qd = 2.92
NLB said:They are related by the Bjorken Sum rule, which says that the sum of the spin of the quarks is equal to the spin of the nucleon. Experiment proved this to be not true.
NLB said:I assume the spin crisis relates to the magnetic moment of the quarks being different from what theory predicted, which are the numbers Ipetrich posted.
NLB said:If the spin of a quark is 1/2 and the spin of a nucleon is 1/2, then there is no "Nucleon Spin Crisis".
NLB said:They are related by the Bjorken Sum rule, which says that the sum of the spin of the quarks is equal to the spin of the nucleon. Experiment proved this to be not true. I assume the spin crisis relates to the magnetic moment of the quarks being different from what theory predicted, which are the numbers Ipetrich posted.
No; we did not give you experimental data but just commented on wrong ideas; there are Terrabytes of experimental dataNLB said:* There's no experimental data.
There are theoretical estimates; all what we were saying ways that quark or bag model estimates are too naive and are not suitable for an explanation (a theory that explains 50% of the data but fails to explain the other 50% is not really helpful - even if your interest is in the first 50%)NLB said:* There's no theoretical estimate either.
There is only one theory today - QCD - and in QCD there are no such ambiguities. Explaining the spin structures based on (non-rel.) quark models is like explaining black holes based on Newtonian gravityNLB said:... it is controversial depending on the definition of a quark and what specific theory we are using
There is a clear relation and I just quoted the correct formula using the g-factor; what I was saying is that I can't see how the quark magnetic moment and the nucleon spin are related; it was your claim that this should be the case, and therefore expected some explanation, reference, whateverNLB said:* Spins and magnetic moments have no relation to each other.
Yes, I think I used that formula, but I can't see how it may help; you either explain the nucleon magnetic moment in terms of its spin (which you can't as long as you can't explain the spin), or you explain the quark magnetic moment in terms of its spin which is trivial and not the subject of the 'spin crisis'.NLB said:* There is, however, an equation that relates them directly: "magnetic moment is defined as μ = g (q/2m) s = g q/4m with s = 1/2"
No, g = 2 + QED corrections, m for 'up'and 'down' is a few MeV; and you can find a lot of data for quark masses at the particle data group; but this is (afaik) irrelevant for the nuclon spinNLB said:* In regards to the above equations, g and m are unknowns for quarks.
I don't think it's muddy thinking. The problem is that all naive models fail to explain the spin, and that even in QCD not everything is well-understood.NLB said:How can it be even after over 25 years, that no one noticed that this is just muddy thinking?
lpetrich said:... One can easily find the magnetic moment:
mup = (4*muu - mud)/3
mun = (4*mud - muu)/3
With
mup = 2.79
mun = -1.81
in nuclear magnetons,
muu = 1.85
mud = -0.97
Dividing by the quark charges,
muu/qu = 2.78
mud/qd = 2.92
A 5% discrepancy.
I spent some time looking for bag-model and lattice-QCD estimates, but I couldn't find very much.
... It's about the results of deep-inelastic-scattering experiments. At typical DIS-experiment momenta, only about 30% of a nucleon's spin is carried in the valence quarks.
In a sense you DO detect quarks experimentally.edguy99 said:If you cannot detect quarks by themselves, what logic is used to experimentally detect an amount of spin or a magnetic moment to the quarks?
The quark magnetic moment is a measure of the strength and direction of a quark's magnetic field.
The quark magnetic moment is measured by studying the behavior of particles containing quarks in a magnetic field.
The quark magnetic moment is an important property of quarks that helps us understand their behavior and interactions with other particles.
The quark magnetic moment is one of the fundamental properties that determine the structure and properties of matter at the subatomic level, along with other properties such as mass and charge.
No, the quark magnetic moment can vary depending on the type of quark and the energy level at which it is measured. It is also affected by the strong nuclear force, which can cause fluctuations in its value.