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Re: more on BCAL light yield estimates
Dear all,
Let me also add some input to these arguments:few years ago I have done
exactly what Alex did:I took the transmission spectra measured in Regina
and available in the portal for different lengths of fibers and for blue
and green fibers digitized them after normalizing to the tails and
furthermore I have multiplied by a typical Bialkali QE (all as a function
of lambda ). After the product was done then I observed the following:
at 5cm the green gave as much light as the blue
but at 175cm (the longest length available) the green was only 75% of the
blue.This was also verfied by us with a rough experiment using UV light
and green/blue fibers.So our conclusion was that the green fiber is not
justifiable for a PM read-out.
Concerning the absolute numbers ,with different MC we always got
collection efficiency from both sides of the fiber higher than 9% so we
always assumed that it was 9% per side.
But I do agree that the spectrum after 2m of (175cm) has to be normalized
to the 2cm one-absolute measurement-and then multiplied by the functional
SiPM or PM efficiency to arrive at the right numbers.
Cheers,Christine
> Dear Colleagues
>
> It is important for us to understand the apparent factor of 4 discrepancy
> between the photoelectron yield estimates and measurements for
> cosmic rays using the BCAL test module. I find the same factor of
> 4 (roughly) as George -- but I get there by a somewhat different path.
>
> Please read the attached and comment.
>
> Our goal should be to produce a note on our understanding of light
> yields since setting specifications for the fibers and SiPM's depend
> on this. In my role as Design Report editor I will generate this note
> with help and input from others. I will also be spending the first week
> of December in Regina working with my good friends there on the BCAL
> section of the Design Report.
>
> Cheers
> Alex
> --
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
> Alex R. Dzierba
> Chancellor's Professor of Physics (Emeritus)
> Department of Physics / Indiana U / Bloomington IN 47405 / 812-855-9421
> JLab Visiting Fellow
> Jefferson Lab / 12000 Jefferson Ave / Newport News, VA 23606 /
> 757-269-7577
> Home Phone: 812-825-4063 Cell: 812-327-1881 Fax: 866-541-1263
> http://dustbunny.physics.indiana.edu/~dzierba/
> ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~