CLAS
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As shown in chapter 3.1, the particle detection efficiency
depends on a number of factors, such as gas refraction index,
its transparency, mirror reflection efficiency, PMT quantum
efficiency and mirror optics.
In order to separate geometry factors from gas and mirror properties,
the number of effective photons
was calculated.
Here 
is the radiator
gas transmissivity for a photon trajectory length
,
is the mirror reflectivity for
reflections, and
is the PMT quantum efficiency.
Fig. 12 shows the PMT quantum efficiency as a function of the wavelength (stars). Open circles and open triangles represent the minimum and maximum quantum efficiencies of a group of seven PMTs tested at Jefferson Laboratory. The parameterization used in our simulation is in reasonable agreement with the measured data.
It is convenient to represent
in the form
where
is the number of the emitted effective photons per
of electron trajectory, and
is the mirror reflectivity, which
is applied during ray-tracing at every reflecting surface.
We note, that
, and
meter.
For
gas and the new optics scheme these numbers
are found to be
The value of
used
in the particle detection efficiency calculations was reduced from
previous estimations for Freon-12 gas and was set at
.
The absolute accuracy of
or
is estimated at about
, therefore
the figures shown can be considered as a conservative estimate.
All particle efficiencies were recomputed for
gas and the modified geometry of the CLAS Cerenkov detector.