All Questions
Tagged with quantum-chromodynamics particle-physics
207
questions
2
votes
0
answers
62
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How are we sure that the measured proton spin puzzle will be also observed similarly in the neutron thus a neutron spin puzzle?
The EMC experiment in 1988 using muons' deep inelastic scattering, has reported that the contribution of the valence quarks triplet (i.e. up-up-down) in the proton was measured to contribute as little ...
- 4,170
2
votes
1
answer
317
views
How Do Pions Mediate The Residual Strong Force?
I know that the continuous exchange of gluons between quarks is what holds hadrons together, and that the exchange of pions between nucleons is what creates the strong residual force. However, how ...
- 375
-3
votes
1
answer
209
views
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?
- 31
1
vote
1
answer
109
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Quark mass dependence of Glueball masses
In pure QCD, we have glueballs. Pure QCD can also be thought of as QCD where the fermion masses have been sent to infinity. If we vary the fermion masses (say, for simplicity, we deal with a single ...
- 6,896
0
votes
1
answer
185
views
How does the Nambu-Goldstone mode explain the absence of parity doubling?
I've been doing some reading about chiral symmetry breaking since it was not touched in my particle physics course
I found these slides
As explained in the above link, if we take $|\psi \rangle$ as ...
- 3,464
3
votes
0
answers
267
views
Why is the chiral condensate a negative quantity?
The chiral condensate serves as an order parameter for the chiral phase transition. Thus, it is a finite quantity in one phase and vanishes in the other phase. It is given as a vacuum expectation ...
- 457
0
votes
2
answers
154
views
What makes up and down quarks so special?
One of the ways a lot of different mesons and baryons are grouped is by their up and down quark content. There's also isospin, which is admittedly a subset of a more general symmetry. But the ...
- 1,405
0
votes
1
answer
454
views
Hadronization time
In the process of hadronization what is the characteristic time? I was thinking about at the inverse of $\Lambda_{\rm QCD}$ but can also be a dependence from $\sqrt{s}$. Can anyone help me?
- 496
6
votes
1
answer
273
views
Photon-Gluon annihilation in QCD
I am starting to learn about QCD, and I wanted to calculate the squared matrix elements for photon-gluon annihilation into a quark and an anti-quark. However, I am having trouble writing down the ...
- 305
6
votes
0
answers
235
views
Which explanation of the OZI rule is correct (or most important)?
The OZI rule states that a QCD diagram is suppressed if it can be cut into two by only cutting gluon lines (the precise wording is addressed in the question What is the precise statement of the OZI ...
- 585
14
votes
5
answers
2k
views
Why aren't all quarks clumped together in one giant hadron?
As far as I am aware, the strong interaction is attractive only, and its carrier, the gluon, is massless meaning it has unlimited range. If this is the case, how come we only observe quarks in pairs ...
- 451
2
votes
1
answer
91
views
How is the colour quantum number not conserved in this process?
I stumbled upon this CERN article, where I found this diagram describing the process $gg \rightarrow HH$:
I'm still new to QCD, and I don't see how a coloured gluon can decay into colourless final ...
0
votes
1
answer
89
views
Color factor in Breit-Wigner formula
We are given the Breit-Wigner formula for the process $ud\rightarrow W\rightarrow e\nu$ as $$\sigma=\frac{1}{N_c^2}\frac{2J_W+1}{(2J_u+1)(2J_d+1)}\frac{4\pi}{s}\frac{\Gamma_{ud}\Gamma_{e\nu}}{(\sqrt{s}...
- 2,122
2
votes
1
answer
169
views
Does pionium decay in massless QCD?
The bound state of ${\pi}^+ {\pi}^-$ is called Pionium.
Is Pionium an Electromagnetic bound state or a Strong Force one? then Why?
Does such a bound state last forever if one works in QCD with ...
- 1,268
3
votes
1
answer
170
views
$U(1)_A$ effects on the baryons?
We know that the axial $U(1)_A$ is anomalous thus not a global symmetry. Therefore there is no direct associated pseudo goldstone boson for $U(1)_A$. This makes the $\eta'$ much more massive than the ...
- 4,336