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

[Marco Mirazita]

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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