[Olympus] rates in TOFs

[Richard G Milner]

Hi Alexander,
I would like to understand better the rates in the TOFs following yesterday's
discussion at the weekly meeting.  In particular, the rates in each TOF for the
following conditions are of interest:

beam off:
Here one is sensitive to HV and threshold settings, light leaks, bad connections
etc.

beam on/no gas:
Here one is sensitive to the tune of the beam and background (non-target elastic
processes). Presumably, we need to develop a clean tune of the beam, involving
adjustment of the slits, centering of the beam in the target cell, etc.  Tuning
scintillators around the beam pipe are very useful to set this up.  We need to
minimize the singles rates in the TOFs.  I think doing this at 4 GeV to start
would be a very significant first step. For sure, going to 2 GeV will need some
effort but the procedure should be quite similar.

When last at DESY, I noticed that there is no shielding in front of the
experiment.  For both HERMES and BLAST we had a wall of lead in front of the
experiment to minimize the beam generated background affecting the detector. 
The TOFs are at a significant distance from the beampipe and are unprotected
from background that could be coming down the tunnel. This should be
considered.

I will start to look at the BLAST operational experience.  As suggested
yesterday, tightening the trigger will also improve the situation.

I copy olympus at mit.edu to stimulate discussion and comment.
Thanks,
Richard