Cerenkov Detector Lead Radiator Simulations
Due to the relatively large photon background in the main Cerenkov detectors
(See Yongguang's Report in the Qweak Document Database), it was decided
that we consider the possibility of putting a radiator in front of the main Cerenkov
detector (Lead or Tungsten). Simulations for this had been done previously by
Neven and he found about 8% excess noise (Neven's Report), which was considered
too high at that time. In the detector thickness study it was later found
that a minimum of 4% excess noise is reached at a thickness of 1.25 cm, compared
to which the 8% found by Neven no longer seemed so bad.
In Neven's work, the secondary particle shower from the radiator and the
corresponding RMS width in the number of photoelectrons at the PMT cathode
was simulated for two primary electron tracks with specific locations
along the quartz bar, close to either PMT.
The simulations I am presently running will repeat Neven's work for the
final quartz bar dimensions and with the bar illuminated entirely.
The two figures below illustrate the current setup.
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The plots below show some preliminary results.
Figure 1
Figure 2
Figure 3
Figure 4
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Figure 2: Origin vertex of secondary particle along beam. The detector
position is at z = 570 cm. The radiator is located at z = 567.5 cm. Green = photons,
Red = electrons, Blue = positrons.
eps version of this graph.
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Figure 3: Number of secondary electrons per primary event
incident on the radiator, as a function of radiator thickness.
The radiation length for Pb is 0.56 cm.
eps version of this graph.
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Figure 4: Excess noise as a function of radiator thickness.
eps version of this graph.
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