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Signal vs Bkg efficiency plots

  1. Sep 9, 2015 #1

    ChrisVer

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    Gold Member

    What information can one obtain from the plots of the background vs signal efficiency? [itex]\epsilon_{bkg}(\epsilon_{sig})[/itex]?
    In particular I attach some plots I made by hand and I want to understand how to obtain what each tells us.
     

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  3. Sep 9, 2015 #2

    mfb

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    2016 Award

    Staff: Mentor

    Your plot should have 1/(background efficiency) or 1-(background efficiency) as vertical axis.

    Each point on the curve is a possible selection. As an example, you can randomly take 60% of the events, then you have 60% signal efficiency and keep 60% of the background. That is not a good selection, of course. Your actual one might keep 90% of the signal events and keep only 5% of the background. If you make the selection a bit looser, you get 91% of the signal, but 10% of the background. Make this in a continuous way (with TMVA usually) and you get a curve. With the usual choices for axes, all curves should look like the blue one.
     
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