Number of p.e. and SiPM requirements

[Elton Smith <elton@jlab.org>]

Hi George,

I have been reviewing the SensL proposal for further development of the
SiPM and realize that we need to come to grips with the observed number of
photoelectrons. This is not a new concern, it is a reflection of the fact
that the measured number of p.e. for cosmic-rays is lower than what we had
originally expected. However, the specifications for the SiPMs are based
on the earlier numbers (GlueX-doc-795), and these are directing future
effort.

Let me summarize the status as I see it. Please set me straight if I am
missing anything:

1. Measured number of p.e. for a minimum ionizing particle is 22-25 per
4 cm of readout, or ~ 6p.e./cm. For normal incident muon (radially in the
detector), this corresponds to 6p.e./cm x 22.5 cm = 135 p.e.
See http://www.jlab.org/ccc/mail_archives/HALLD/halld-cal/msg00288.html

2. The number used in GlueX-doc-795 is 863 p.e. (See Table 2, row 6 col
4). This corresponds to 5082 p.e./GeV x 0.17 GeV/muon = 863 p.e. The basis
for the 42,279/GeVx0.12 comes from GlueX-doc-808, p. 5.

-> The measured number is lower than the original expectation by 863/135 =
6.4. If we use the measured number, then this is equivalent to using PDE
valueswhich are 6.4 times SMALLER than those assumed in GlueX-doc-795.
This has substantial impact on the resolution as well as implications for
specifications on the readout.

Am I missing anything?

Thanks, Elton.


Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625