For a while we were worried about the functionality of the VT compiled GEANT. These plots compare VT compiled and Jefferson Lab compiled photon rates. Starting at the left, the first plot shows the total photon rates at each detector, as well as the rates due to each process, for three energy ranges. Note that at each detector the highest rate seems to be from high energy Moller electrons. The second plot shows the total photon rates at each detector, using the Jlab compiled GEANT and the old collimator. The last figure shows the total photon rates at each detector, using the Jlab compiled GEANT and the NEW collimator. It looks like the difference in rate is due to the new collimator!
To see photon rates from different processes at middle chambers:
Smallest energy range
Middle energy range
Highest energy range
Figure 1
The following figure is a log-log plot of photon rate/MeV vs. photon energy at the GEM, middle and back chamber locations. Note that most of the rate at the GEM location seems to come from high energy photons.
To see separate GEM and chambers log plots:
Photon Spectra at GEMs
Photon Spectra at chambers
To see spectra plots by process (with harsh E cuts):
GEMs
Middle Chambers
Back Chambers
Figure 2
An investigation of the ep elastic cuts for use in calculating photon rates reveals several problems. The x and y cuts for each detector are shown as red lines on each plot. On the left, we see an example of cuts around the ep elastic peak that seem to cut on the photons nicely. The figure on the right, however, demonstrates two possible problems. One is in the shower y position plot. The photon rate seems to be flat, so varying the ep 'box' size will change the photon rate due to target showers, but at least it will do so in a linear way. In the ep elastic x position plot, if the lower x cut were reduced, the rate would increase drastically. This would also be a problem with the shower x and y positions for detector 1.
To see all the plots, go here.
An explanation for the shower triple peak shape is that the octant that we are interested in is actually seeing photons that are coming from the other collimator aperatures. This seems to be supported by Figure 4. Figrure 5 shows why there is a dip in the detector 3 rate vs. detetector 4. Detector 3 is positioned directly after the second collimator, while detector 4 is further away and sees a higher rate in general, as well as being more sensitive to the ep-peak cuts.
Figure 3 a, 3b
Figure 4
Figure 5
The following plots show the rates with the 1 cm of argon photon attenuation factored in; note they are 500X smaller, less than 10 kHz. The photon attenuation length parameterization for argon used in the calculation of these rates (From Figure 11.1 in PDB 1994) is shown to the right.
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Here is a picture of the position of the vacuum window relative to the target and first collimator box.
Figure 8
