[Hps-ecal] pedestals and pileup

[Andrea Celentano]

Hi Nathan,
this is a very interesting study. I'd like to add a comment to the 
discussion (something we already mentioned some time ago at one of the 
Ecal meetings)

- In FADC mode 7, for every event and for every channell over threshold, 
we record 4 numbers:
* Energy (in FADC counts, i.e the sum of the samples around the signal peak)
* Time
* Pedestal (average of the first 4 samples, in FADC counts)
* Signal amplitude (in FADC counts, i.e. the max signal height)

We can think about 2 ways of subtracting the pedestal using these data

1) Event by event, as energy - pedestal * fadc_integration_window_width
2) On average, computing the average pedestal for a given channel over 
the run, and then subtracting it as before

If we expect the pedestal to be roughly constant during a run (if the 
beam current is constant), then I expect the second solution to be 
better than the first one.
With the first solution, event by event the pedestal noise affects the 
energy resolution.


Andrea

On 01/10/2015 10:48 PM, Nathan Baltzell wrote:
> Hi Everyone,
>
> Here is a recent look at some pedestal studies.  It appears they have an effect from pileup.
> It’s not significant for many channels, but for high rate channels near the beam I think we
> are going to want to correct it.  It would be interesting to see if Luca’s gain calibration sees
> any current-dependence coming from incorrect pedestals.
>
> -Nathan
>
>
>
>
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