ATLAS inclusive and sliced samples (eg W+jets)

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Discussion Overview

The discussion revolves around the concepts of inclusive and sliced samples in the context of Monte Carlo (MC) generators used in high-energy physics. Participants explore the implications of using these different types of samples for statistical analysis and event generation across various energy ranges.

Discussion Character

  • Technical explanation
  • Debate/contested
  • Mathematical reasoning

Main Points Raised

  • Some participants question the distinction between inclusive and sliced samples, suggesting that the sum of sliced samples should equal the inclusive sample.
  • Others argue that generating an inclusive sample requires a vast number of events, particularly at high energies, which can be inefficient due to the predominance of low-energy events.
  • It is proposed that creating multiple sliced samples allows for better management of event statistics across different energy ranges.
  • Participants discuss the need for weighting when combining sliced samples to form a single spectrum, emphasizing the importance of cross sections in this process.
  • There is a suggestion that if the inclusive sample is independent, it could be added to improve statistics in the low-energy range.
  • Concerns are raised about potential double-counting when combining inclusive and sliced samples, with a participant noting that sliced samples are subsets of inclusive samples.
  • Correct merging of samples is highlighted as necessary to avoid double counting, with specific criteria for vetoing certain events mentioned.

Areas of Agreement / Disagreement

Participants express varying views on the relationship between inclusive and sliced samples, with some agreeing on the need for independent samples while others emphasize the potential for double counting. The discussion remains unresolved regarding the best approach to combining these samples.

Contextual Notes

Participants note that the generation of events is heavily influenced by the energy range being studied, and the efficiency of sample production can vary significantly based on the chosen method. There are also unresolved considerations regarding the criteria for merging samples and the implications of event independence.

ChrisVer
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I have a small technical question, if anyone has ever worked with it...
What does inclusive and sliced samples mean (at a MC generator)? I have seen that the sliced samples are divided according to mass slices for the different processes, but the inclusive are not. Why would they give such samples separated? I mean as I see it, wouldn't the sum of the sliced samples be the "inclusive" one?
Thanks.
 
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ChrisVer said:
I mean as I see it, wouldn't the sum of the sliced samples be the "inclusive" one?
Not necessarily. Imagine you want to describe some process in the range of 100 GeV to 4 TeV (pT, pT sum, invariant mass - doesn't matter here). To get a reasonable statistics at 4 TeV with an inclusive sample, you might need billions of events. Most of them are at low energy, where you have more events than you can ever hope to process: simulations of detector response are a significant fraction of the overall CPU hours used for high-energy physics.
Making multiple separate samples, each with appropriate size, reduces the number of events significantly. To get a single spectrum, you have to multiply them with some weight before you can add them.
 
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mfb said:
Not necessarily. Imagine you want to describe some process in the range of 100 GeV to 4 TeV (pT, pT sum, invariant mass - doesn't matter here). To get a reasonable statistics at 4 TeV with an inclusive sample, you might need billions of events

Agree on that, and somehow it helps me understand the inclusive samples. And I agree that at 4TeV you will need some billions of events too.

mfb said:
Most of them are at low energy, where you have more events than you can ever hope to process: simulations of detector response are a significant fraction of the overall CPU hours used for high-energy physics.

aha, nice... so getting the necessary events at high energies you will get several orders of magnitude more events at low ones too, making the generation of events extremely slow.

mfb said:
Making multiple separate samples, each with appropriate size, reduces the number of events significantly. To get a single spectrum, you have to multiply them with some weight before you can add them.

Yes I agree, the weight should take into account the different cross sections...
However if you add them in order to get the overall background you expect at let's say 0.1-4TeV , would you add appart from the sliced samples the inclusive one as well?
 
ChrisVer said:
Agree on that, and somehow it helps me understand the inclusive samples. And I agree that at 4TeV you will need some billions of events too.
You don't need billions of events at high energy, but you need events everywhere.

To get 1000 around 4 TeV, you might need billions events in total. It is more effective to produce 10000 in the range of 4 TeV, 10000 in the range of 3 TeV and so on.
In terms of luminosity, the highest sample might correspond to something like 20+ times the data luminosity, the other samples can be lower as statistics is not so crucial there any more.

If the inclusive sample is independent, it can get added. It can improve the statistics in the low-energetic range.
 
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mfb said:
If the inclusive sample is independent, it can get added. It can improve the statistics in the low-energetic range.

Wouldn't that however count as a double-counting?
 
mfb said:
If the inclusive sample is independent
!
 
A sliced sample is a sub sample of the inclusive, so they are not independent.

Combining samples requires a correct merging, where certain events would be vetoed according to a double counting criterion.
 

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