[Primexd] [EXTERNAL] Re: Question

[Shepherd, Matthew]

Igal,

(sending again from the right address)

On May 14, 2020, at 1:55 PM, Igal Jaegle <ijaegle at jlab.org<mailto:ijaegle at jlab.org>> wrote:

Matt,

Where is stored the real threshold in the database?

It is encoded in the pedestal which is in the database.

As noted before this is tricky because threshold in simulation and threshold in data are applied in fundamentally different ways.

One must realize we use a flash ADC not an integrating ADC so in real life the threshold is applied to the pulse amplitude.  However, it is the integral of the pulse that is calibrated to energy.  The relationship between amplitude and integral is well-approximated by a constant but has some variations, especially for the small pulses at threshold.

So, we take the true pedestal (from data) and the typical pedestal RMS, and we know the DAQ threshold in units of the least significant bit of the fADC.  And based on this we simulate the threshold on amplitude.  But then we need to convert this to an energy as the simulation only "knows" about energy (and it is the integral that is used for energy in the data anyway).  So we use the peak to integral ratio and the gain (again from data) to create an effective threshold energy.

There some variances, e.g., the pedestal RMS and also variation of the peak-to-integral ratio.  They get convolved together, I believe we have put in a parameter (also in the DB) to get that variation on average correct.  It isn't clear they (especially the peak to integral ratio) are highly dependent on channel or could be quantified in a way that provides a significantly improved picture of reality.

Matt


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