# How to present the charges of quarks with the following Nc?

#### HerrBlatt

Homework Statement
Assume that quarks are presented in SU(Nc) with a unknown dimension of Nc, and define the rate Rμ of the scattering cross sections between e+e- -> hadrons(here, consider u, d, s, c, b quark) and e+e- -> μ+ μ-. Give out the result of Rμ with Nc. See detailed equations below.
Homework Equations
Rμ = σ（e+e- -> hadrons）/ σ(e+e- -> μ+μ- )
I have already known the cross sections can be presented like this.
σ（e+e- -> hadrons）∝ Σ eq^2 & σ(e+e- -> μ+μ- ) ∝ e^2,
where eq is the charge of a certain quark(u, d, s, c or b)
But I don't know the relationship between Nc and eq.

(This is my first time to post a thread. I don't know how to insert a equation typed in LaTex or Word, so it may be a little tired to read...
I'm so sorry about that and thank you for help!)

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#### mfb

Mentor
What does the sum run over for hadrons? It is not just the flavor. How is that related to the symmetry group?

You can use LaTeX with $.$a^2$->$a^2##

#### HerrBlatt

You mean it also runs over colors? And we should multiply a Nc on it? In this way the sum will be 11/9 Nc?

#### mfb

Mentor
You mean it also runs over colors?
Right. More colors -> more hadrons.
I'm not sure where the 11/9 came from.

"How to present the charges of quarks with the following Nc?"

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