Technical Note
radphi-1998-901
meson in the presence of significant
electromagnetic and charged hadronic backgrounds. Experience during
commissioning has shown that of the two, the former is by far the most
serious limitation faced by the experiment. Calculations based upon data
from early beam tests in 1997 indicated that the experiment would saturate
in terms of its trigger efficiency over an order of magnitude below the flux
needed to achieve the sensitivity required by the physics. The situation
was subsequently improved by installation of a helium bag and shielding,
and during 1998 commissioning the situation was reassessed by careful
measurements. This report details the analysis of these data in terms of
a mathematical model for our electronics, along with checks that verify the
model. It also shows what improvements will be required to approach the
efficiency demanded in order to run effectively near the design beam flux of
photons/s, and suggests a surprising simplification to our
trigger that would achieve this end.
This note is divided into two parts. The first describes the formulae that are being used to model the experimental rates and compares them with measurements as a test of their validity. The second is concerned with how the model extrapolates to the beam intensities at which the experiment was designed to run, and what should be done to optimize the trigger for efficient operation under these conditions.