Understanding Tau Identification in ATLAS: A Brief Overview

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Discussion Overview

The discussion revolves around the identification of tau particles in the ATLAS experiment, specifically focusing on the tau identification methods described in referenced papers. Participants explore concepts such as inverse background efficiency, likelihood scores, and the reconstruction of hadronic tau events.

Discussion Character

  • Technical explanation
  • Conceptual clarification
  • Debate/contested

Main Points Raised

  • One participant seeks clarification on the definitions of inverse background efficiency and likelihood score, expressing confusion about their implications in the context of figures from a referenced paper.
  • Another participant explains that inverse background efficiency, or rejection rate, indicates how many background events are misidentified as signal, noting that higher signal efficiency leads to lower inverse background efficiency.
  • The same participant describes how boosted decision trees (BDT) provide numerical values for events, with larger values indicating more signal-like characteristics, and explains the relationship between cut values and the resulting points in the figures.
  • A further inquiry is made regarding the reconstruction of hadronic tau, questioning whether the barycenter represents a disk within a specified radius and how the vertex coordinate system is determined from jet trajectories.
  • One participant questions the choice of source material, suggesting that a more comprehensive reference exists than the one being used.

Areas of Agreement / Disagreement

Participants express differing views on the appropriateness of the source material and the interpretation of technical concepts, indicating that multiple perspectives exist without a clear consensus.

Contextual Notes

There are limitations in understanding the definitions and implications of terms like inverse background efficiency and likelihood score, as well as the specifics of tau reconstruction methods. The discussion also highlights potential dependencies on the definitions used in the referenced papers.

Who May Find This Useful

Researchers and students interested in particle physics, specifically those studying tau identification techniques in high-energy physics experiments like ATLAS.

ChrisVer
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I have some questions concerning this paper (mainly about the tau identification):
http://arxiv.org/pdf/1201.5466v1.pdf

especially the figures 3-6...

I don't understand what is the inverse background efficiency, neither the likelihood score. As a result, I am unable to understand what info the figures give. Any help?
 
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Inverse background efficiency is also called the rejection rate. A value of 100 means you identify 1 out of 100 background events as signal.
The higher the signal efficiency you want to be, the more events you have to keep, which means you will identify more background events as signal, which gives a lower inverse background efficiency.
The different curves are different tau decay modes, pT regions, background samples and so on.

A boosted decision tree will give you a numerical value for each event, where larger values mean "more signal-like". Figure 3 shows the distribution of the BDT outputs for signal and background events. You can then choose different cut values, each cut value will give you one point in the diagrams 4-6.
 
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Thanks,
I still have some further questions in case you can help me.
In the paper I mentioned in the OP (in Sec 2), as well as here
http://arxiv.org/pdf/1409.0343v1.pdf In Sec 2, is mentioned how to reconstruct the hadronic tau.
It says:

A barycenter is formed consisting of the sum of the four-vectors of the constituent topological clusters, assuming zero mass for each of the constituents. Then, the τ_had detector axis is calculated by using clusters within ∆R =...< 0.2 around the barycenter. The four-vectors of those clusters are recalculated using the tau vertex coordinate system and the vectors are summed up.

Does that mean that the barycenter is like a disk within the ∆R<0.2 ?
And by that you are able to identify the vertex coordinate system by running back the jet's trajectory and see where the trajectories intersect?
So then you know they should come from taus and you are able to sum the jet's four vectors and calculate the tau's energy?
 
Why are you using a few page proceedings as your source when it references a more complete note?
 

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