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Re: Npe/GeV
HI Alex,
The implication from this analysis is that we should expect a factor of 2
more light from production 'green' calorimeter modules. If this is
correct, then our requirements on the PDE from the SiPMs can be relaxed
from our current value of 21% back to the original 12% which is less of a
reach.
George and Zisis: Can you confirm this?
Thanks, Elton.
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Hi Elton
Indeed, one of the reasons George, Zisis and I did the spectral
analysis was to understand that factor of four based on Npe estimates
obtained from the 4-m module (blue fibers) with cosmic rays.
We believe that a factor of two contribution to that factor of
four is illustrated in Fig. 2 of our note. The bulk attenuation length
would lead one to expect a factor of 2 reduction for the source
at the center of the 4m module (2 m of light travel) but the analysis
shows a factor of 4 reduction (loss of the blue light). Another
factor is the capture fraction which had been estimated as
9.3% from GUIDEit. Simple solid angle estimate based on the
critical angle is more like 5% (what the manufacturers quote
as "at least"). Finally, there are uncertainties in transmission through
the interfaces and prism light guide. So the estimates of approx 25
Npe/cell
for the 4-m blue module with cosmics, may not be inconsistent with
the 8000 or so photons/MeV at the source.
But we'll write this all down, with numbers and errors, as you suggest.
Cheers
Alex