Difference: TRTHTmiddleBitTuing (6 vs. 7)

Revision 72015-06-22 - KyungeonChoi

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META TOPICPARENT name="KyungeonChoi"

TRT HT middle bit tuning


Introduction

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Using only the middle of the tree TRT high threshold (HT) bits reduces the effect of pileup under higher instantaneous luminosity conditions during Run 2.
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Using only the middle of the three TRT high threshold (HT) bits reduces the effect of pileup under higher instantaneous luminosity conditions during Run 2.
 Discrepancies in the modelling (timing and width of the high level signal) results in a HT middle bit fraction lower in MC by 3 - 10% depending on the TRT region. Since TRT particle identification is now based on using only the middle HT bit, the goal of this study is to tune the TRT digitization to improve the agreement between data and simulation.
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The definition of HT middle bit fraction, applied in any region of interest, is as follows:
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The definition of HT middle bit fraction, applied in any region of interest, is as follows:
  HT middle bit fraction ≡ number of HT hits with middle HT bit high / total number of HT hits
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  • for data
    asetup 17.2.5.2,AtlasProduction,here
  • for MC
    asetup 19.2.1.2,AtlasProduction,slc6,here
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Hopefully we can have another look at this when we have the Run 2 13TeV data and MC - using the same releases
 

Digitization

Two TRT_Digitization tags which are related to the study.

  • TRT_Digitization-01-00-14
    • The baseline TRT digitization tag for tuning study.
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    • (Most) tuning parameters are overrided in
      postInclude.OverrideTRTparameters.py
    • HT shaping is tabulated in ??''?? and has to be hard-coded.
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    • (Most) tuning parameters are overrided in
      share/postInclude.OverrideTRTparameters.py
    • HT shaping is tabulated in
      src/TRTElectronicsProcessing.cxx
      and has to be hard-coded.
 
  • TRT_Digitization-01-00-24
    • The tag which all final tuning parameters are implemented.
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Tuning of high threshold ΔT0 shift

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Since there is an additional shaping circuitry for high threshold, high threshold T0 setting can be differ from the overall (or low threshold) T0 setting. Tuning of high threshold T0 setting is done by an additional T0 shift on top of overall T0 setting. The shift is applied after discrimination so that it has a discrete step of 0.78125 ns Discussion: 1. The step of 0.78125 ns exists before and after discrimination - I'd simply state that this is the step size. 2. Does it matter if the shift is applied before or after the call to DiscriminatorResponse() ? I guess not since it is the middle bit we are only interested in.
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Since there is an additional shaping circuitry for high threshold, high threshold T0 setting can be differ from the overall (or low threshold) T0 setting. Tuning of high threshold T0 setting is done by an additional T0 shift on top of overall T0 setting. The shift can be applied with a step of 0.78125 ns.
 (See Andrew's slides for the detail). The implementation can be applied for each TRT partitions: Barrel short, Barrel long, Endcap A-wheel and Endcap B-wheel.

The following figure shows data and MC agreement for the HT middle bit fraction as a function of HT ΔT0 shift. Different colors represent each TRT partitions, and empty squares have intersection point(s) with a red dashed line which means perfect data and MC agreement. Red arrows indicate possible HT ΔT0 shifts from original digitization setting. Barrel short is straightforward since it has only one point of intersection, but the other three TRT partitions have two points of intersections. The HT bit pattern distribution can be used to determine better HT ΔT0 shifts as shown below.

 
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