Re: BCAL beam test and Npe estimates (fwd from George)

[Elton Smith <elton@jlab.org>]

---------- Forwarded message ----------
Date: Mon, 16 Apr 2007 10:28:44 -0600
From: George Lolos <George.Lolos@uregina.ca>
To: dzierba@indiana.edu, elke@jlab.org, elton@jlab.org,
     Zisis Papandreou <Zisis.Papandreou@uregina.ca>
Cc: George Lolos <George.Lolos@uregina.ca>
Subject: Re: BCAL beam test and Npe estimates

Hi Alex:

I would expect that shower fluctuations play a major role in the overall
number of photons but they dominate the cell numbers the most.  One can
see that from the first three figures in the report I sent last week.  I
always believed that the total number of photons deposited in the BCAL
is less prone to such drastic fluctuations because the e-m shower energy
has to go somewhere.  This can also be seen in the fluctuations in the
first three figures in the main cells the shower is expected to
contribute.  For example, in figure 2 and cells (as shown in the figure
not as the BCAL will read them out) 4-8, the probability that a track
will enter the cell is > 90%so even if we multiply the probability by
the mean number of photons, we end up with a large number.

I am still baffled and I start suspecting poor coupling of PMT-light
guide - BCAL with air gap(s) in effect between light guide and silicon
cookies.  It only takes a microscopic break in index of refraction from
1.6 to 1.0 to greatly reduce the number of photons entering the PMT.
But, again, I amy be wrong.

Cheers,

George

>>> Alex Dzierba <dzierba@indiana.edu> 04/16/07 8:52 AM >>>
Hi All

After talking to George about evidence that there was plenty of light
from the BCAL module in the beam test - it seems that the apparently
small estimate of Npe from using mean/sigma for ADC's is really a
measure of shower fluctuations dominating.  This what George has
been telling us all along.

Alex
-- 
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
Alex R. Dzierba
Chancellor's Professor of Physics (Emeritus)
Department of Physics / Indiana U / Bloomington IN 47405 / 812-855-9421
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