[d2n-analysis-talk] BB cer peds

[Brad Sawatzky]

On Tue, 26 Jan 2010, posik at jlab.org wrote:

>  I am now looking at the beginning of the d2n experiment and trying to
> find the pedestal locations of ADC signals. I should note that over this
> run period we were using the 792 ADC. I found one ped run from early Feb.
> run 1087. I attached the plots of that run below.

Any 'cosmics' run will also give us good pedestals for the Cerenkov.

Just FYI.  I did some beam tests where I explicitly looked for pedestal
stability vs. pulse rate in the PMT (where the pulses were due to
beam-related backgrounds).  The results showed that the mean pedestal
position was very stable, but that the width of the pedestal increased
with PMT rate.  That is basically what you expect.

The good news is that it tells you that the pedestals you get with beam
off (or cosmics, etc), are what you should use with beam too.

>  Since there was a lot of changing during this period, I wanted to look at
> the peds for other runs. I decided to look at run 1258 which is a onepass
> H2 run and to check the ped I plotted ADC from PMT 1 and I used a T8 cut
> "(DBB.evtypebits&1<<8)==(1<<8)" on an ADC spectrum. What remains after
> that pulser cut is three peaks in the ADC (blue curve in
> elastic_ped.png). To get a better under standing of where the ped is, I
> decided to plot the same ADC and apply a T2 and TDC cut and see if I can
> see a threshold(this is the red curve in the elastic_ped.png). I then
> scaled the T8 cut histo to T2+TDC cut histo for comparison. Looking at
> these two histos, there is a suppression in left most peak, does that
> mean that is the ped? But then what about the center and right most
> peaks?

I'm looking at the elastic_ped.png file here.  Based on that plot, the
pedestal value I would use is ~65 channels (the center of the largest
'middle' peak).  The box/devil-horns structure is noise messing up the
pedestal.

Applying a T2 cut will reduce the pedestal:signal ratio (should get more
signal).  If you normalize to the the 'signal' region, ie. ch > 100 then
you can see that the whole pedestal blob (ch 50--80) is suppressed by
around a factor of 2.

-- Brad

-- 
Brad Sawatzky, PhD <brads at jlab.org>  -<>-  Jefferson Lab / Hall C / C111
  Ph: 757-269-5947 -<>- Pager: 757-584-5947 -<>- Fax: 757-269-7848
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