Geant4 Simulations for the Radon Electric Dipole Moment Search at

30
25
26.3%
Forward Configuration
Back Configuration
Absolute Efficiency (%)
20
15
10
17.5%
9.7%
6.5%
5
0
10 100 1000 10000
γ-ray Energy (keV)
Figure 4.1: Geant4 generated absolute efficiency curve for a ring of eight GRIF-
FIN detectors in the highest efficiency mode (forward configuration) and the fully
suppressed mode (back configuration).
due to various components of the apparatus. Figure 4.3 illustrates the decrease in
efficiency with increasing thicknesses of µMetal shielding.
The efficiency of the RnEDM experiment is extremely important as it is directly
related to the sensitivity of measurement. The precision of the EDM measurement
is limited by the number of photopeak counts detected. The statistical limit for the
frequency measurement [32], introduced in Section 2.3.5, is
√
δ ∆ω = 2 1
T 2 A 2 (1−B) 2 N , (4.1)
where T 2 is the spin-decoherence time, A is the analyzing power for a measurement
that detects a change of counts ∆N = AN, and B is the fraction of N due to
background. The linearity of δ ∆ω (or equivalently σ f ) with T −1
2 and N −1/2 was
studied using the Geant4 simulations and is discussed in Section 4.2.3.
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