All Questions
7
questions
1
vote
0
answers
35
views
Evidence of more generations in the QCD beta function
We know that the beta function for QCD is
$$
\beta = -\left(11 - \dfrac{2N_f}{3}\right),
$$
where $N_f$ is the number of fermions in the theory. We have $\beta_{\text{SM}} = -7$.
Now, my question is, ...
- 1,611
1
vote
1
answer
105
views
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
0
votes
0
answers
121
views
Negative running coupling constant in QCD?
Considering the one-loop running coupling constant in QCD:
$$\alpha_s(\mu) = \frac{a_s(\mu_0)}{1 + \frac{33-2f}{6 \pi}ln\left( \frac{\mu}{\mu_0}\right)}$$
where f is the number of quarks flavours with ...
- 585
0
votes
1
answer
373
views
Calculating strong coupling constant $\alpha_s$
I'm trying to find out how to calculate the value of strong coupling constant. but haven't found any exact answer, all I get is reference to perturbation theory.
is there any exact defined formula to ...
- 141
3
votes
2
answers
681
views
1
vote
1
answer
232
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Why does literature list the strong coupling at the scale of the Z-boson's mass?
In the 2004 edition of the book "QCD as a Theory of Hadrons" by S. Narison, the author provides a value for the strong coupling at a scale of the mass of the Z boson,
$$ \alpha_s (M_Z) = 0.1181 \pm ...
- 2,648
5
votes
1
answer
1k
views
Experimental determination of $\Lambda_{QCD}$
I have a question about $\Lambda_{QCD}$, the energy scale at which there is a transition from the regime of perturbative QCD to quark confinement.
How it is measured experimentally?
- 153