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(warning) Note: The pre-filters and MC samples in this analysis are consistent with the analysis Eric was performing; however, they are significantly different from the data sets and pre-filters Bill applied in designing the Pass6 and Pass7 analyses. For example, these data sets have no cut on FswGamState == 0 and the IrrFilter is different (and almost certainly having unintended consequences).

Introduction

I've gone back to Eric's old page with the hope of picking up where he left off. Of course, this leads to the always enjoyable task of replicating the work that he has already done. The working directory for the previous analysis is:

...

Name

Purpose

Gamma Efficiency

Bkg Efficiency

Cut

IrrFilter

Remove irreducible bkg events

0%

13%

Code Block
((McZDir < -.2 && McId < 20) | (McZDir < .1 & McId > 20))
&& McAcdZEnter > 100 && McCharge !=0 && McTHPosHitOthers < 6

TkrCalCore

Take only "good" events

6.2%

2.2%

Code Block
TkrNumTracks>0 && CalEnergyRaw > 5 && CalCsIRLn>4 && CTBCORE>0.1

AcdEngFilter

Only events with moderate signal in the ACD

0%

47%

Code Block
(AcdTotalEnergy+AcdRibbonEnergy<0.05) && McZDir > 0

Prefilter

Only select relevant events
(warning) !(IrrFilter) is wrong (warning)

6.2%

1.2%

Code Block
(TkrCalCore && !(IrrFilter) && !(AcdEngFilter)

 

nSig

nBkg

Before Prefilters

~9x10^5

~4x10^6

After Prefilters

55015

48614

One very important thing to note here is how confusing the convention of "Cuts" and "Filters" is. There needs to be some standard convention for either keeping or rejecting events that return TRUE for a selection (I believe that Bill uses "Cuts" and "Vetos").

Pass 6 Performance

First defining some ACD variables:

...

These numbers seem to agree well with Eric's results. However, it naively seems like there are still some photons sneaking into the bkg sample. This is because selecting !(IrrFilter) will return True if McCharge == 0 (leaving about ~50 gamma events out of ~550). Putting a cut on McCharge, we now get a background rejection of 1.03%.

Pass 7 Performance

Moving on to Pass7, the ACD analysis has be modified a fair amount. I rebuilt GR v17r35p10 and generated roughly the same number of signal and background events (again using Eric allGamma.txt and background.txt scripts). Since Pass7 was just a re-design of the worksheet, the prefilters should have the same efficiency (Irreducible 13%, AcdEngCut 47%) with a slight change in CalTkrCore since it depends on CTBCore (2.2% for bkg and 6.4% for sig) leaving a total of 1.3% of the bkg and 6.4% of the gamma-ray events.

...

Name

Purpose

Gamma Efficiency

Bkg Efficiency

Cut

BasicTileCut

Reject events with track pointing at struck tile.

94.2%

6.18%

Code Block
Tkr1SSDVeto< 5 && AcdTkr1ActDistTileEnergy > .7 && AcdTkr1ActiveDistENorm> -350

RibbonCut

Reject events with track pointing at struck ribbon.

93%

5.85%

Code Block
(AcdTkr1RibbonActDistENorm > -40  && 
Tkr1SSDVeto < 3 &&  AcdTkr1RibbonActDistMaxTileEnergy  > .04) || 
(AcdTkr1RibbonDist > -1/(CTBBestEnergy/100)  && Tkr1SSDVeto < 2)

TotalTileEnergyCut

Reject events with excess ACD total energy.

88.1%

2.08%

Code Block
AcdTotalTileEventEnergyRatio > .8 || AcdTkr1ActiveDistENorm > -200 && 
AcdTotalTileEventEnergyRatio > max(.005, .1 -  .0001*AcdTkr1ActiveDistENorm) * 
max(1., CTBBestLogEnergy/2.5)

CornerCut

Reject events in the corner gap of the ACD.

86.9%

2.06%

Code Block
((Tkr1LATEdge/1.5)^2 + (AcdCornerDocaENorm - 10)^2 < 6400  && 
Tkr1SSDVeto < 3)
|| (Tkr1LATEdge < 300 && abs(AcdCornerDocaENorm-2) < 4)

TileEdgeCut

Reject events at tile edges with decreased signal.

86.9%

2.06%

Code Block
Tkr1SSDVeto == 0 & abs(AcdTkr1ActiveDistENorm) < 10 & 
AcdTkr1ActDistTileEnergy > .025

VetoTileCut

Reject events with ...

86.6%

1.71%

Code Block
(AcdTkrVActiveDistENorm > -100 && AcdActDistTileEnergy /
sqrt(max(1., CTBBestLogEnergy-3.5)) > .9 +.15* TkrVSSDVeto) ||
 (abs(AcdTkrVActiveDistENorm) < 15 && AcdActDistTileEnergy > .25 && TkrVSSDVeto < 2)

Pass 8 Performance

Generating merit files off of the GlastRelease-HEAD1.1365 version (which came shortly after GlastRelease-v19r3p4), I started by looking at the effect of the Pass7 ACD cuts. Here the prefilters could have changed (since track finding etc. has changed). Using the same cut definitions, I find fairly similar results with slightly worse background rejection.

...

Name

Purpose

Gamma Efficiency

Bkg Efficiency

Cut

VetoHit1Cut

Reject events with best track pointing a struck tile/ribbon

94.5%

14.2%

Code Block
Acd2VetoHit1 < 5.

TotalTileEnergyCut

Reject events with excess ACD total energy

86.5%

2.44%

Code Block
(Acd2TotalTileEventEnergyRatio > .8 || (Acd2Tkr1ActiveDistENorm > -300 && 
Acd2TotalTileEventEnergyRatio > max(.005, .1 - .0001*Acd2Tkr1ActiveDistENorm)))

VetoGap1Cut

Reject events in gaps of the ACD

86.2%

2.42%

Code Block
 Acd2VetoGap1 < 2.

VetoHitCut

Reject events if other track points at hit tile

86.1%

2.35%

Code Block
 Acd2VetoHit < 2.

Conclusions

Well, it doesn't seem like we are where we want to be (not a surprise). It looks like we would like to roughly double the background rejection (1/2 the efficiency) for the Pass 8 analysis with the AcdReconV2 variables. However, it appears that the simple cuts with AcdReconV2 are roughly comparable to those with the original AcdRecon, meaning that the degredation degradation in background rejection is may be in part due to upstream reconstruction changes (which in any case are not yet complete).

Looking Forward

  • Can we easily modify the AcdV2 cuts to increase background rejection with the current reconstruction? Basically, can we optimize these cuts?
  • Right now AcdV2 is using the G4 propagated covariance matrix, which really isn't right for cosmic-rays (since it uses electron hypothesis). Would changing this make an improvement?
  • How do the CalOnly events look? Can we develop some rough background rejection for them?
  • Obviously this will improve as the upstream reconstruction improves. Can we provide any guidance for that?
  • CTs are always the after-burner to get the boosted rejection power that we need.