Cross section

  • Thread starter Jodahr
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  • #1
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Main Question or Discussion Point

Hello,

How can I convert the number of events + the luminosity in a cross section?

I think this must be trivial...

thanks..
 

Answers and Replies

  • #2
2,967
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By dimensional analysis if you know the dimensions of each of the quantities involved.
 
  • #3
10
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ah..lol..I think it's just...events = sigma * luminosity...right?
 
  • #4
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Ok, how did you conclude that?
 
  • #5
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hm?...I wanted to get a cross section limit for monojet signals...and I always found only the luminosity and the events...and event has no dimension..luminosity is inverse barn and XS is barn..so..if I really only need those paramaters..then it's trivial...I thought maybe I also need sth else...
 
  • #6
2,967
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Usually luminosity is a flux density, with dimension L-2 T-1, instead of dimension L-2. Thus, what we get as a result proportional to luminosity is not # of events, but, instead, an event rate (# events per unit time) with a dimension T-2.

The proportionality constant must have a dimension L2. However, the proportionality constant should be proportional to the number of scatterers, which is dimensionless. The proportionality constant corresponding to ONE scatterer is a characteristic of the dynamics of the scattering event, and is customarily referred to as a cross-section.

What I tried to say could be summarized as:
[tex]
\frac{d N_{\mathrm{reactons}}}{d t} = K \, \mathcal{L}
[/tex]
where [itex]\mathcal{L}[/itex] is the luminosity of the incident beam, and:
[tex]
K = N_{\mathrm{scatters}} \, \sigma
[/tex]
where [itex] N_{\mathrm{scatters}}[/itex] is the total number of scatterers in the target, and [itex]\sigma[/itex] is the total scattering cross-section for a single scattering event.
 
  • #7
10
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Thanks a lot...
but I think in the paper I have read they have used the integrated luminosity...because they have used exactly the dimension "inverse barn"...
 
  • #8
34,234
10,278
"Integrated luminosity" is sometimes just called "luminosity" - wrong, but shorter, and fine for talks/meetings and so on, where it is clear what is meant. In papers and other publications, it should be called "integrated luminosity" everywhere.
 

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