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

[Marco Mirazita]

Hi Tyler,
thank you, I will look at the data tomorrow.
Marco


Il 2021-11-03 16:45 Tyler Lemon ha scritto:
> 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