Hi Brad,<br><br> Here are the peds from an LED and a fivepass run with ~8uA current, both taken on the 1881 ADC.<br><br>LED beam line side:<br><a href="http://jlab.org/~posik/d2n/BB/cer/peds/led/1829.png">http://jlab.org/~posik/d2n/BB/cer/peds/led/1829.png</a><br>
<br>LED RHRS side:<br><a href="http://jlab.org/~posik/d2n/BB/cer/peds/led/1834.png">http://jlab.org/~posik/d2n/BB/cer/peds/led/1834.png</a><br><br>fivepass beam line side:<br><a href="http://jlab.org/~posik/d2n/BB/cer/peds/fivepass/1849_beam.png">http://jlab.org/~posik/d2n/BB/cer/peds/fivepass/1849_beam.png</a><br>
<br>fivepass rhrs side:<br><a href="http://jlab.org/~posik/d2n/BB/cer/peds/fivepass/1849_RHRS.png">http://jlab.org/~posik/d2n/BB/cer/peds/fivepass/1849_RHRS.png</a><br><br>I will get working looking at the peds over all hardware changes as you suggested in the previous email. Been a little slow with the APS talk.<br>
<br>-matt<br><br><div class="gmail_quote">On Mon, Feb 8, 2010 at 11:16 AM, Brad Sawatzky <<a href="mailto:brads@jlab.org">brads@jlab.org</a>> wrote:<br><blockquote class="gmail_quote">
<div class="im">On Fri, 05 Feb 2010, <a href="mailto:posik@jlab.org">posik@jlab.org</a> wrote:<br>
<br>
> So I looked at the Big bite cerenkov ped location for run 1849, which<br>
> is a He3 production run at ~8-9 uA. I did this by plotting the ADC<br>
> for the first 100,000 events and making a T8 trigger cut (pulser)<br>
> which is "(DBB.evtypebits&1<<8)==(1<<8)". Using this cut, I then fit a<br>
> Gaussian to the ped and extract the mean. Then I compared these "beam<br>
> on" ped positions with those of the LED runs. Here is a list of the<br>
> mean ped values:<br>
</div>[ . . . ]<br>
<br>
Interesting. Good work! Please generate a couple of slides showing the<br>
LED-run pedestals overlaid on top of the beam pedestals for the 20 PMTs.<br>
I'd like to see how the characteristics of the pedestal change.<br>
<br>
Also, we need to determine if the pedestals change between the LED runs<br>
and what you show here is due to beam loading or something else. Look<br>
for a cosmics/no-beam run in this period and redo your pedestal checks<br>
(and generate the above plots) for a beam-off run and an adjacent<br>
beam-on run.<br>
<br>
If you can find appropriate runs, here's what would be ideal:<br>
A) peds with beam-off (cosmics or rest run)<br>
B) peds at low current (1 uA or so)<br>
C) peds at full current<br>
Having A-C for each hardware configuration (v792, 1881, with pre-amp on<br>
beamline side, without pre-amp on beamline side). would help<br>
disentangle configuration from beam-loading effects.<br>
<div class="im"><br>
> You can see that there is a significant ped drift with the beam line<br>
> side pmts (1-10) from the LED peds, and the RHRS side (pmts 11-20) are<br>
> fairly close to the LED peds. I also calculated the rates for this<br>
> run, using TDC hits and cutting away beam trips, here are the results:<br>
</div>[ . . . ]<br>
<div class="im">Rate for cell 05: 0.9315 MHz<br>
------------------------<br>
Rate for cell 06: 0.4108 MHz<br>
------------------------<br>
Rate for cell 07: 1.0756 MHz<br>
------------------------<br>
Rate for cell 08: 0.7693 MHz<br>
------------------------<br>
Rate for cell 09: 0.9036 MHz<br>
------------------------<br>
Rate for cell 10: 0.7387 MHz<br>
------------------------<br>
Rate for cell 11: 0.1087 MHz<br>
------------------------<br>
Rate for cell 12: 0.0224 MHz<br>
------------------------<br>
Rate for cell 13: 0.0802 MHz<br>
------------------------<br>
Rate for cell 14: 0.0816 MHz<br>
</div>[ . . . ]<br>
<div class="im"><br>
> pmt 6 and 12 seem to be much lower than the rest of the pmts on that<br>
> side. This was also seen in run 1848.<br>
<br>
</div>There was some Pb shielding installed at the beamline height on the<br>
beamline side. The shadow should have been cast over more than PMTs 6,<br>
12 though... I'm not sure what's going on there.<br>
<br>
I don't think I beleive the 20kHz number associated with cell 12.<br>
There's either a bug in the calculation, or the hardware is doing<br>
something really strange.<br>
<div class="im"><br>
> Using these ped values as well as mirror and TDC cuts I plotted the<br>
> ADC for mirror 3 (1849_mir3_pe.png) and 12 (1849_mir12_pe.png) for run<br>
> 1849. Please note that the x-axis is in #p.e. The red histo is the<br>
> signal and blue histo is an off mirror background. Mirror 3 shows<br>
> about 4-6 p.e and mirror 12 7-8 p.e. I am thinking about including<br>
> these two images in my APS talk.<br>
<br>
</div>Using PMT 12 as a 'representative' histogram probably isn't a good idea.<br>
What do 11 and 13 look like?<br>
<div class="im"><br>
> So since the ped were stable with beam on/off with the v792 ADC, then<br>
> that means the 1881 ADC is responsible for the ped shift. I assume<br>
> then is has to do with the electronic differences between the 792 and<br>
> 1881. I was wondering what exactly this difference is that results in<br>
> the ped location shifting with beam on/off?<br>
<br>
</div>I did the with/without beam pedestal stability test before Transversity.<br>
All I can say is that it was stable then. That was with the v792s and<br>
with no extra amplification on the beamline side PMTs...<br>
<br>
I suspect/hope that the difference you see is due to some other change<br>
that happened at the same time. The tests mentioned at the top of the<br>
email should clarify things.<br>
<font color="#888888"><br>
-- Brad<br>
</font><div><div></div><div class="h5"><br>
--<br>
Brad Sawatzky, PhD <<a href="mailto:brads@jlab.org">brads@jlab.org</a>> -<>- Jefferson Lab / Hall C / C111<br>
Ph: 757-269-5947 -<>- Pager: 757-584-5947 -<>- Fax: 757-269-7848<br>
The most exciting phrase to hear in science, the one that heralds new<br>
discoveries, is not "Eureka!" but "That's funny..." -- Isaac Asimov<br>
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</div></div></blockquote></div><br><br clear="all"><br>-- <br>Matthew Posik<br>Email: <a href="mailto:posik@temple.edu">posik@temple.edu</a><br>Temple University Physics Dept.<br>Office: BA-319<br>Office #: 215-204-1331 <br>
<br>