Granularity of readout with fine-mesh pmts

[Elton Smith <elton@jlab.org>]

Dear Zisis,

On Monday we decided to pursue a conceptual design for the readout of the
Bcal usign fine-mesh pmts. I have sketched out some arrangements for the
pmts using Hamamatsu's tube assemblies H6152-70 and H8409-70 for the 1"
and 1.5" pmt tubes respectively. With the dimensions for these assemblies,
the face of the bcal only allows a 3x3 matrix (compared to 4x6) for the
inner and 2x2 matrix (as before) for the outer layers. Below is a table
with a comparison of photocathode coverage for the nominal and this new
proposal. I have also posted the sketches on the wiki at
http://www.jlab.org/Hall-D/software/wiki/index.php/Alternative_readout

Given the geometrical constraints, when you review the issue of
granularity could you specifically consider a 3x3 arrangement? What is
compromised by reducing the granularity by this amount? Can we say how it
impacts photon reconstruction?

Comments are welcome as we try to evaluate the various issues that affect
the operation of the detector with the revised readout scheme.

Thanks, Elton.


Photocathode coverage of nominal and fine-mesh pmt options:
--------------------------------------------------------------------------

Nominal design

         full area     Detectors           cathode   Fraction
inner     111.6 cm2    24 SiPM 1.44cm2     34.6 cm2   0.31
outer     113.4 cm2    4 XP2262 D=4.4cm    60.8 cm2   0.53


Fine-mesh pmts Option.
Note: Nine of the smallest 1" pmts bearly fit with housing over the inner
face. Four 1.5" pmts can fit over the outer face.

         full area     Detectors             cathode   Fraction
inner     111.6 cm2    9 H6152-70 D=1.75cm   21.6 cm2   0.19
outer     113.4 cm2    4 H8409-70 D=2.7cm    22.9 cm2   0.20


Elton Smith
Jefferson Lab MS 12H5
12000 Jefferson Ave
Suite # 16
Newport News, VA 23606
elton@jlab.org
(757) 269-7625
(757) 269-6331 fax