All Questions
24
questions
0
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81
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Why is there a $u$ in the middle of the feynman diagram for a quark and an antiquark annihilating?
There is a feynman diagram in chapter 2 of Griffiths Introduction to elementary particles, where a pair annihilation is taking place. I am confused as before it was written that internal lines are ...
- 11
1
vote
0
answers
77
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Energy stored in the gluon fields -- in a proton, versus, in a pure Yang-Mills mass gap
I was reading this How much of the proton's mass is due to the Higgs field? and finds the discussion says:
As Prof. Strassler explains in the link above, the proton mass is best throught of as ...
- 593
1
vote
2
answers
154
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The ratio of the Higgs and QCD condensate contribution to valence quark masses
According to https://en.wikipedia.org/wiki/Quark#Mass, the quarks have the following masses.
I suppose these data in the table shows the valence quark masses, such that the uud valence three quark ...
- 4,336
1
vote
4
answers
778
views
What's the difference between an electron and a quark?
Could you explain how QFT defines the peculiarity and differences, as to charge, between an electron and a quark?
A quark has a fractional charge. Is the Coulomb force proportional to these charges? ...
- 691
1
vote
1
answer
288
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Fundamental Particles (Quarks) and Quantum Fields
From what I have understood while studying quantum and particle physics is that all the particles are excitations of their respective fields.
This makes me wonder if elementary particles like quarks ...
- 33
4
votes
1
answer
851
views
Why are some Cabibbo-Kobayashi-Maskawa (CKM) matrix elements equal?
I'm simply asking what theoretical origins are behind 'coincidences' in CKM matrix elements, such as the decay of charm to strange quarks, and the decay of up to down quarks both having a coupling of $...
- 2,604
2
votes
3
answers
698
views
Do quarks annihilate into photons or virtual gluons?
I initially assumed a quark and its anti quark would annihilate into 2 photons (like electrons with positrons) and this does seem to be the case at least sometimes (e.g. For $\pi^0$s).
However in our ...
- 2,604
0
votes
1
answer
105
views
Why does quark scattering obey the Rutherford formula for pointlike particles when they have a finite spatial wavefunction distribution?
In our particles physics course there is this graph that shows that quark scattering cross sections (labelled QCD) obey the Rutherford scattering formula for pointlike particles.
However, even though ...
- 2,604
0
votes
1
answer
1k
views
Top quark decay rate calculation $\Gamma(t\rightarrow W^+b)$
I'm trying to calculate the disintegration rate $\Gamma(t\rightarrow W^+b)$ from the Fermi Diagram:
I know the lagrangian for the interaction would be:
$$ -iF = \bar{u_b}\gamma^\mu P_Li\frac{g}{\...
- 27
2
votes
1
answer
131
views
Why does the term $i\epsilon^{\alpha\mu\beta\nu}p_{\alpha}q_{\beta}$ vanish in the squared amplitude of the top decay?
I would like to calculate the squared of the amplitude of a top-decay $t-> Wb$. I know already the solution, but I can't get there: I get stuck with the Levi-Civita-Tensor on my way. Can you help ...
- 45
5
votes
1
answer
279
views
Why do the $c$, $b$ & $t$ quarks have strong hypercharge?
From the $SU(3)$ flavour symmetry we have quantum numbers for the up, down and strange quark, associated with the Eigenvalues of the Gell-Mann matrices $\lambda_3$ and $\lambda_8$. Namely $\lambda_3$ ...
- 75
4
votes
2
answers
321
views
How are composite hadron fields related to elementary quark fields?
(This question is related to: A pedagogical exposition of the hadron physics?)
I'm a mathematician who has been trying to learn quantum field theory for a while. I've gone through large parts of ...
- 421
4
votes
1
answer
223
views
Well colour me surprised$.$
I was reading Scharf's Quantum Gauge Theories: A True Ghost Story when I stumbled upon the following paragraph (p. 118):
The standard example of a gauge theory with massless gauge fields is the ...
3
votes
2
answers
730
views
Why doesn't infrared slavery provide a proof for quark confinement?
It is well known how and why the running coupling of QCD grows as we reduce energy or equivalently increase distance. Hence, if the effective color charge increases with distance then why doesn't this ...
- 17.8k
6
votes
2
answers
445
views
Measuring and calculating free quark masses
Particle data book contains masses of the free quarks. I wonder, how do experimentalists determine the masses of the free quarks even though they are trapped inside hadrons (except perhaps in quark-...
- 26.8k