[dsg-hallb_rich] [EXTERNAL] Re: d0 measurement procedure

[Tyler Lemon]

Hi Marco,

I took sets of measurements with both CCDs covered with lens caps, putting the CCDs in as dark as possible conditions.

For each CCD, there are two sets of measurements, one set of at least 60 measurements taken about one minute apart over the course of an hour with exposure times of 0.5 ms and a second of 10 measurements taken with 975-ms exposure times (maximum I could do with ximea-shot), each measurement taken about one minute apart.

The data are on ifarm at the path below. I also put the shell script I wrote to automate the periodic ximea-shot commands in that directory.

/w/hallb-scifs17exp/clas12/tlemon/RICH-II/bkg-study

Each data set is in a separate subdirectory whose name specifies what CCD was used and what exposure time was used. The CCDs are noted as "other-ccd" or "original-ccd" to keep with the naming convention from the set of measurements we did after swapping CCDs.

-Tyler
________________________________
From: Marco Mirazita <Marco.Mirazita at lnf.infn.it>
Sent: Monday, October 25, 2021 10:07 AM
To: Tyler Lemon <tlemon at jlab.org>
Cc: dsg-hallb_rich at jlab.org <dsg-hallb_rich at jlab.org>; rich at jlab.org <rich at jlab.org>; Contalbrigo, Marco <mcontalb at fe.infn.it>
Subject: [EXTERNAL] Re: [dsg-hallb_rich] d0 measurement procedure

Hi all,
I did some more studies on the measurements we took so far, comparing
with the similar measurements done for RICH-1. See the attached pdf.
My main conclusions are the following

1) We have now about 3 order of of magnitude more background than when
we measured the mirrors of RICH-1
2) There are fluctuations in the background level of the order of 10%
from one measurement to another
3) Given such huge amount of background, even small fluctuations can
heavily affect the analysis of the data with light on, making the D0
result questionable
4) The second CCD ("other-ccd" data taken on Oct. 20) has about a factor
of 2 less background. This seems to suggest that a large fraction of the
increased background come from the CCD itself. But I cannot exclude a
large contribution also from the ambient.
5) The wave in the y-projection of the background-subtracted spot images
at minimum that I showed Friday seems to be associated to the spot
itself. Moving away from the minimum the waves in the unsubtracted
images are much more similar to the ones we see in the bkg data. Again,
this may indicate a problem with the CCD, perhaps due to locally high
light levels.


I suggest to take some measurement with both CCD totally covered with
black sheet. This will give us the zero level of the cameras.

Best regards,
Marco

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