Reconstruction vs Identification

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Discussion Overview

The discussion centers on the concepts of reconstruction and identification in the context of jet analysis in particle physics. Participants explore the definitions, processes, and distinctions between these two terms, examining their roles in experimental setups.

Discussion Character

  • Exploratory
  • Technical explanation
  • Debate/contested

Main Points Raised

  • One participant seeks clarification on the distinction between reconstruction and identification, suggesting that reconstruction involves applying selection criteria to classify an object as a jet.
  • Another participant confirms that reconstruction identifies potential jet candidates, while identification further assesses these candidates against additional criteria to determine their validity.
  • It is noted that generic jets may not require stringent identification criteria, as many objects with energy deposits in the calorimeter are classified as jets.
  • Identification can utilize a Boosted Decision Tree (BDT), but it is also mentioned that this is not a strict requirement.
  • A participant questions the necessity of BDTs for identification, suggesting that identification should yield a probability of the particle's identity, which BDTs typically provide.
  • Another participant proposes that instead of using BDTs, one could apply cuts on the variables for identification.
  • It is acknowledged that even when using BDTs, the output is often treated as a binary decision (yes/no) based on a cut on the BDT output.

Areas of Agreement / Disagreement

Participants express differing views on the necessity and application of BDTs in the identification process, indicating that there is no consensus on the best approach to distinguish between reconstruction and identification.

Contextual Notes

The discussion highlights potential ambiguities in the definitions and processes of reconstruction and identification, as well as the varying criteria applied in different contexts. The role of BDTs and alternative methods for identification remains a point of contention.

ChrisVer
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This is a fast-question/need of confirmation concerning the two: Reconstruction and Identification.
I am trying to "separate" what they mean.
For example when we reconstruct a jet, we apply several selection criteria that the object "jet" should satisfy. Is that correct? Then any object that satisfies those criteria is reconstructed as a jet and used as one afterwards. My confusion comes here because this implies an identification; the object is seen as a jet afterwards. Or I should better say reco-jet.
Identification on the other hand is also using other selection criteria + some variables fed in a BDT (or LLH) that are used to identify the jet as a fake (maybe from a tau) or not?

If the above is "correct" (if it's wrong then I have misunderstood something crucial), I don't see the reason for applying the two and not just going for ID alone. it's like going from city A (bulk events) to B("known" event type and kinematics) by passing first from another city C (reconstruction), rather than taking the straight way to B.
Thanks
 
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ChrisVer said:
For example when we reconstruct a jet, we apply several selection criteria that the object "jet" should satisfy. Is that correct?
Right.

Reconstruction and identification are not always clearly separated. Experimentally, you often have a two-step process. Reconstrution gives you "here, this could be a jet" and identification then says "okay, this jet candidate is probably from the right primary vertex and satisfies some other quality criteria".
Generic jets don't have strong identification criteria, because nearly everything with energy deposit in the calorimeter is called a jet. The distinction is clearer for everything else.

Identification can use a BDT but does not have to.
 
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mfb said:
Identification can use a BDT but does not have to.
hmm... I can't see that...
Wouldn't the ID come with a probability that the particle is what it's IDed with? I thought that BDT does that immediately by separating bkg to signal (and result to loose,medium or tight IDs). Is there an alternative way?
 
ah... I think instead of feeding the variables in a BDT you could apply cuts on them...
 
ChrisVer said:
ah... I think instead of feeding the variables in a BDT you could apply cuts on them...
Right.
And even with a BDT, the output is often used as "yes/no" - a cut on the BDT output.
 

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