[Hps-ecal] pedestals and pileup

[Nathan Baltzell]

Hi Andrea,

I think you are right:  we should use the pedestal from mode-7 data.  And there is a 3rd
option I mentioned on page 3 that I think may be better than event-by-event or run-averaged:
keep a running average of the pedestal over the last N seconds/events.

-Nathan


On Jan 11, 2015, at 6:48 AM, Andrea Celentano <andrea.celentano at ge.infn.it> wrote:

> 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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>