[d2n-analysis-talk] BB cer ped shifts

[posik at jlab.org]

Hi Brad,

   So I looked at the Big bite cerenkov ped location for run 1849, which
is a He3 production run at ~8-9 uA.  I did this by plotting the ADC for
the first 100,000 events and making a T8 trigger cut (pulser) which is
"(DBB.evtypebits&1<<8)==(1<<8)". Using this cut, I then fit a Gaussian
to the ped and extract the mean. Then I compared these "beam on" ped
positions with those of the LED runs. Here is a list of the mean ped
values:

pmt  Beam On         LED
     --------     -----------
01      393.401       483
02      346.358       407
03      246.901       397
04      356.24        478
05      478.192       537
06      454.217       498
07      534.134       598
08      461.678       526
09      301.158       458
10      329.81        466
11      295.913	      300
12      422.566       425
13      509.785       516
14	573.247       579
15	570.353       580
16	438.798       444
17	375.965       390
18	532.975       526
19	319.83        316
20	406.072       398

You can see that there is a significant ped drift with the beam line side
pmts (1-10) from the LED peds, and the RHRS side (pmts 11-20) are fairly
close to the LED peds. I also calculated the rates for this run, using TDC
hits and cutting away beam trips, here are the results:

Run 1849
current ~8uA
He3 5-pass
Beam Trip cut


Rate for cell 01:    0.5599 MHz
------------------------
Rate for cell 02:    0.7269 MHz
------------------------
Rate for cell 03:    0.9418 MHz
------------------------
Rate for cell 04:    1.0396 MHz
------------------------
Rate for cell 05:    0.9315 MHz
------------------------
Rate for cell 06:    0.4108 MHz
------------------------
Rate for cell 07:    1.0756 MHz
------------------------
Rate for cell 08:    0.7693 MHz
------------------------
Rate for cell 09:    0.9036 MHz
------------------------
Rate for cell 10:    0.7387 MHz
------------------------
Rate for cell 11:    0.1087 MHz
------------------------
Rate for cell 12:    0.0224 MHz
------------------------
Rate for cell 13:    0.0802 MHz
------------------------
Rate for cell 14:    0.0816 MHz
------------------------
Rate for cell 15:    0.1121 MHz
------------------------
Rate for cell 16:    0.0622 MHz
------------------------
Rate for cell 17:    0.7178 MHz
------------------------
Rate for cell 18:    0.1007 MHz
------------------------
Rate for cell 19:    0.0903 MHz
------------------------
Rate for cell 20:    0.0889 MHz
------------------------

pmt 6 and 12 seem to be much lower than the rest of the pmts on that side.
This was also seen in run 1848.


 Does any one have any suggestions why this may be? Is there extra
shielding in that region that pmt 6 and 12 don't see as much rate as the
rest?

I also checked this ped shift for pmt 3 with run 1850 and could not see a
clear ped, so I did a quick replay (first 100,000 events) of 1851 and the
ped location for pmt 3 was at chan. 250.

Using these ped values as well as mirror and TDC cuts I plotted the ADC
for mirror 3 (1849_mir3_pe.png) and 12 (1849_mir12_pe.png) for run 1849.
Please note that the x-axis is in #p.e. The red histo is the signal and
blue histo is an off mirror background. Mirror 3 shows about 4-6 p.e and
mirror 12 7-8 p.e. I am thinking about including these two images in my
APS talk.

So since the ped were stable with beam on/off with the v792 ADC, then that
means the 1881 ADC is responsible for the ped shift. I assume then is has
to do with the electronic differences between the 792 and 1881. I was
wondering what exactly this difference is that results in the ped location
shifting with beam on/off?

-matt


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