Bug #19343

Hit finding at the edge of a waveform gives inconsistent results

Added by Gianluca Petrillo almost 3 years ago. Updated almost 3 years ago.

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The fitter PeakFitterGaussian (larreco:source:larreco/HitFinder/HitFinderTools/ can have questionable fits set the peak outside the fitted range. This can be indeed close to correct if the region of interest was wrongly determined, or if the waveform suddenly truncates (as it may happen e.g. for a out-of-time cosmic ray depositing energy late in the event).

For example, event 3, channel #2281, ticks 2993-2999 from SBND simulation file /pnfs/sbnd/persistent/ContinuousIntegration/reference/standard/reco_basic/nucosmics_reco_basic_test_sbndcode_Reference-201803090902.root contain a partial hit whose fit apparently sets the center of the hit at 3001, outside the range of the hit itself.
The region of fit is highlighted in green: -0.601 -1.907 -3.990 -6.033 -6.844 -5.295 -0.843 6.121 14.279 21.804 27.024 (the last digit available, 27.024, is sample 2999). The result is:

Hit #2694:  Channel  2281 View =   1 Signal type =   0 Wire =  C:0 T:0 P:1 W:295
        StartTick =    2993     EndTick =    2999       PeakTime = 3001.00 +/-  300.10  RMS =    5.33
        Amplitude = 1085123075017539584.00 +/- 108512305783767040.00    Integral = 3831844752043540480.00 +/- 205155263286607872.00     ADCsum =   29.22        Multiplicity =     0 of 1       GoodnessOfFit = 4000.00 DoF =       1

Depending on the machine, the result may be senseless (as the amplitude in this fit) or sensible (the same hit was elsewhere reconstructed as ample 4.23 calibrated ADC counts).

This edge case should be reconsidered, and in particular the fitter could declare failure to fit and produce no hits.


#1 Updated by Tracy Usher almost 3 years ago

There are some cases where the output of the fits does not make sense but I think these should be trapped either by the end user (e.g. perhaps starting to take the chi-square/dof seriously) or in the peak fitter where it might recognize bad parameters being handed to it before the actual attempt to fit.

Do you have statistics on how big an issue this is for SBND?

#2 Updated by Lynn Garren almost 3 years ago

  • Status changed from New to Feedback

#3 Updated by Gianluca Petrillo almost 3 years ago

No, sorry.
This sounds like something that could emit a warning in LArG4, like if the peak of the activity is behind the end of the waveform by less than one σ (defined by longitudinal diffusion).

#4 Updated by Katherine Lato almost 3 years ago

  • Assignee set to Andrzej Szelc

Email exchange:
ok. Why don't you assign it to me for now, and I'll try to see how bad
it is (now that, thanks to Gianluca, I understand what the problem is).


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