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-- KevinLynch - 30 Apr 2008

Production Fitter Studies

Before launching expanded production, it would be nice to confirm that the production fitter itself is not introducing unacceptably large systematic effects to the lifetime. Indeed, many of these studies can not be done with the production pulse output, but must be done with special "hooks" into the guts of the fitter, because you must extract information or correlations that you don't want in the output trees. There are additional studies that can be done with the production pulse output, but not with the general histograms already in use.

These are studies that must be done independently on each production fitter, as they depend on the details of the fitter implementation; they can't be shared across fitters.

Linearity Studies

A fitter must pass a number of linearity requirements. I don't think these need to be terribly stringent requirements, but we must know that the output is close to linear (or the fitter is likely missing pulses in a systematic way) and that the linearity doesn't change early-to-late (or the fitter is likely time shifting pulses early to late in a systematic way). The fitter should be studied for:

  • linearity on the sub-tick scale
  • linearity within the island
  • linearity within the fill
  • linearity across different fitting methods

Fitting Method comparisons

There is no reason to assume, a priori, that different fitting methods (fast fitting, Brent's minimization, weighted fits, etc) in the production code will produce the same time spectra; comparisons must be made, and the impact of systematic differences on the lifetime must be understood. The different fitting methods should be studied for:

  • systematic time correlations between all methods
  • systematic amplitude correlations between all methods
  • systematic pedestal correlations between all methods
  • systematic pedestal/amplitude/time correlations for all methods individually

Fitting Method Choice

One must understand the potential systematic timing shifts that might be introduced early-to-late if the mix of fitters changes early-to-late (as it likely will). The fitter choice must be studied for:

  • choice on the sub-tick scale
  • choice within the island
  • choice within the fill
  • choice by amplitude (raw and fitted)
  • choice by pedestal (raw and fitted)
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Topic revision: r1 - 2008-04-30 - KevinLynch
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