All Questions
Tagged with quantum-chromodynamics standard-model
155
questions
-1
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Superposition of charge states in the Neutral Pion
The quarks of neutral pions don't exist in a pure flavour state, and instead are described as a superposition of up-antiup with down-antidown:
$\frac{u\bar{u}-d\bar{d}}{\sqrt{2}}$
However up and down ...
- 115
4
votes
1
answer
302
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Global symmetries QCD goldstone bosons
Beside the local $SU(3)$-Color-symmetrie The QCD Lagrangian also has global symmetries:
$$L_{QCD}=\sum_{f,c}\bar{q_{fc}}(i\gamma^\mu D_\mu - m ) q_{fc} - \frac{1}{4}F^a_{\mu \nu} F^{a \mu \nu} $$
$SU(...
- 63
3
votes
1
answer
530
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Why do gluon jets have more particles?
From papers on the concept of quark/gluon jet tagging, I've seen that gluon jets have more particles and a broader radiation pattern. Why does carrying more color charge allow them to produce more ...
- 979
9
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2
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286
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Why are protons/neutrons spin-$\frac{1}{2}$ when they are made up of three valence quarks (also spin-$\frac{1}{2}$)?
If we take the composite angular momentum of the three valence quarks, we should have a proton/neutron spin angular momentum of,
$$S=\{ \frac{1}{2},\frac{3}{2} \}$$
using the general rule for adding ...
- 941
3
votes
1
answer
213
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What gives rise to mass gap for gluons, even if they are massless?
It is known that QED does not have a mass gap.
On the other hand, at the heuristic level, QCD has a mass gap.
But photons and gluons are both "massless". Could anyone explain (at least at ...
- 1,669
0
votes
1
answer
100
views
Is there an energy release from gluon expansion and contraction?
When an electron drops to a lower orbit, energy is released as a photon. Gluons expand and contract in-between quarks, described like springs or rubber bands that have tremendous force when extended ...
- 4,783
1
vote
1
answer
81
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How can I show the following contraction of the electromagnetic field strength and its dual? [closed]
Given the electromagnetic field strength $F^{\mu\nu}$, and its dual $$\tilde{F}^{\mu\nu} =\dfrac{1}{2}\varepsilon^{\mu\nu\alpha\beta}F_{\alpha\beta},$$
how can I show that
$$\tilde{F}^{\mu\nu}F_{\nu\...
6
votes
3
answers
2k
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Can free quarks exist?
I know that currently free quarks do not exist but can they exist under any circumstance? The Physicsworld article Quarks break free at two trillion degrees states that they do but I want a ...
- 61
0
votes
1
answer
83
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Are glueballs confined without a connection to quarks?
Without being bound to quarks through the strong force, is there any reason why glue balls would be confined? Are they confined
- 4,783
5
votes
4
answers
668
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Why are gluons color charged but not photon? Could there be a charged EM force carriers like gluons or neutral color charge carrier like photon?
Gluons have a color charge why don't photons have an electric charge like gluons?
1
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1
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60
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$\alpha_s$ strength in quarkonium potential energy formula
The top answer to Is there an equation for the strong nuclear force? explains that there is a coulomb's law-like formula:
$V(r)=−\frac{4}{3}\frac{α_s(r)ℏc}{r}+kr$
that describes how quarks and ...
- 451
1
vote
1
answer
105
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Why is there still disagreement over the mass of the bottom (or beauty) quark, but none of the others?
Wikipedia (among other places) lists two values for the alleged mass of the B quark, 4.18 and 4.65 GeV.
Only one of the two possible masses listed has a link to another Wiki page explaining the ...
- 4,509
1
vote
1
answer
168
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Why is "a phase for the QCD vacuum" considered a fundamental constant and what does it even mean?
We can read about fundamental physical constants in Wikipedia:
There is, however, no single "correct" way of enumerating them, as it is a matter of arbitrary choice which quantities are ...
1
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0
answers
106
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Do quarks have a non-zero electric dipole moment?
It is written here, in this PSE link that an electron has a measured perfect spherical charge density therefore a zero electric dipole moment (i.e. perfect monopole charge).
My question is, are quarks ...
- 4,170
-3
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1
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Do Quarks Exist?
Do Quarks Really Exist?
Is there any experiment which can confirm the existence of Quarks and what kind of force is that which binds them to form neutron and proton?
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