Instantaneous Lumi and Integrated Lumi

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Discussion Overview

The discussion revolves around the conversion of Instantaneous Luminosity (L_t) to Integrated Luminosity (L) in the context of particle physics, specifically related to data collection from experiments such as those at the LHC. Participants explore the implications of time spans in these calculations and the significance of units involved.

Discussion Character

  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant presents a formula for converting Instantaneous Luminosity to Integrated Luminosity and shares a specific calculation that yields a seemingly nonsensical result.
  • Another participant clarifies that the integrated luminosity should be calculated over a relevant time span, suggesting that the initial calculation was based on a single event rather than a broader time frame.
  • A question is raised about the necessity of knowing the time-span of data collection to accurately translate between integrated and instantaneous luminosity.
  • There is a comparison made to speed calculations in everyday scenarios, emphasizing the importance of time in determining rates.
  • A humorous remark is made regarding the implications of speed and time in a driving analogy, highlighting the confusion in the original luminosity calculation.

Areas of Agreement / Disagreement

Participants express differing views on the calculation of integrated luminosity, particularly regarding the necessity of a time span for accurate conversion. The discussion remains unresolved, with multiple perspectives on the implications of the calculations presented.

Contextual Notes

Limitations include the dependence on the time span of data collection and the potential for confusion regarding units when dividing luminosity by time.

ChrisVer
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I have a pretty basic question...
How can you convert the Instantaneous Luminosity [itex]L_t[/itex] to the integrated Luminosity [itex]L[/itex]?
I know that the relation is the following:
[itex]L = \int L_t dt[/itex]
but if the time is [itex]\sim 25~ns[/itex] and [itex]L_t = 1.7 \times 10^{34} ~cm^{-2} s^{-1}[/itex], then I get an integrated luminosity of:
[itex]L=42.5 \times 10^{25} ~cm^{-2} = 4.25 \times 10^{-13} fb^{-1}[/itex]
which doesn't make sense as a number... dividing with the time gives a more sensible result but right now I don't see why.
 
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You calculated the integrated luminosity from a single LHC bunch-crossing.
If you want the integrated luminosity collected within a day, you have to take a day as time.

Dividing luminosity by time gives wrong units, how can that be more sensible?
 
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So in general it's impossible without knowing the time-span of your data-collection to translate your integrated luminosity to the instantaneous one? (the reverse of the above)

As for the units, true... I got to use sleepnessless as an excuse.
 
ChrisVer said:
So in general it's impossible without knowing the time-span of your data-collection to translate your integrated luminosity to the instantaneous one? (the reverse of the above)
Can you tell how fast I went in my car, traveling 30 km, if I don't tell you how long I was traveling?
 
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mfb said:
Can you tell how fast I went in my car, traveling 30 km, if I don't tell you how long I was traveling?

Officer, I can't have been going 80 miles per hour! I've only been driving ten minutes!
 
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