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Figure 5:
UPV OR scaler rate vs. beam current measured at the
beginning of the June run period.
![\begin{figure}\begin{center}\mbox{\epsfxsize =9.0cm\epsffile{upvB.eps}}\end{center}\end{figure}](img28.png) |
Figure 6:
UPV OR scaler rate vs. beam current measured at
the end of the June run period.
![\begin{figure}\begin{center}\mbox{\epsfxsize =9.0cm\epsffile{upvC.eps}}\end{center}\end{figure}](img29.png) |
The rates in the upstream veto wall run a factor of 20-40 lower than
the tagger OR. The UPV OR is formed by a OR'ing together the outputs
from the 8 discriminators connected to the UPV counters. The width
of the UPV OR signal is assumed to be the same as that of
the CPV. The observed scaler rate
for the UPV OR is given in
the model by
where
is the rate in the UPV OR per nA of beam current.
The value of
varied by as much as a factor of 5, depending
upon the quality of the beam tune and what CLAS was doing. The
scan shown in Fig. 5 taken towards the beginning of the June
period under average beam conditions should be contrasted with the
scan shown in Fig. 6 during which CLAS emptied their
hydrogen target. Under no circumstance did the UPV OR rate rise
high enough that nonlinear effects from electronics dead time became
observable. This implies a restriction on the validity of the model
to rates where the UPV OR is below 5-10MHz. Under worst-case conditions
this implies a maximum beam current of 360nA, well above our design
luminosity that corresponds with this radiator to 250nA. The other
restriction of the model is that the veto window width is wide enough
to exclude the entire coincidence peak (see Eq. 6),
which implies a lower limit on
of roughly 15ns (see
Fig. 18 below).
In analogy with the classification of events as either trues or
accidentals with respect to the tagger, each event is also classified
as either a Uhit or Umiss event, depending upon whether
or not whatever produced the hit in the RPD shared the same mother
photon as something that produced a hit over threshold in the UPV.
The quantities
[
] represent the
fractions of events in each class which fall within the UPV coincidence
window. As before, one assumes in the definition of Uhit events that
the causal chain connecting the RPD and UPV hits is a few tens of ns
long at most.
Next: the CPV OR
Up: The model
Previous: the RPD OR
Richard T. Jones
2003-02-12