Geant4 Simulations for the Radon Electric Dipole Moment Search at

6
5
linear regression:
y = 0.005926 x - 1.3452e-04
4
σ f
(e-04 Hz)
3
2
1
0
0.05 0.06 0.07 0.08 0.09 0.1
T2 -1 (sec -1 )
Figure 4.10: The sensitivity of the fitted frequency versus the simulated spindecoherence
time (T 2 ). The linear behaviour validates the statistical precision equation
(see Equation 4.1) for the RnEDM measurement.
4.2.3 Statistical Limit
The validity of Equation 4.1 was explored using Geant4. According to Equation4.1
thesensitivity in thefrequency improves linearly with N −1
2 andT −1
2 , where N
is the number of counts and T 2 is the spin-decoherence time. Figure 4.10 confirms the
linearity of the sensitivity in the frequency with the inverse of the spin-decoherence
times T 2 . In these simulations the most intense 592 keV γ ray was fit over 30 seconds
with varying spin-decoherence times ranging from 10 to 20 seconds. The fits were
similar to the example given in Table 4.1 with the spin-decoherence times fixed to the
simulated values. Similarly, Figure 4.11 confirms the linearity of the sensitivity with
N −1/2 . In these simulations the full 223 Rn decay was simulated up to a maximum
number of 4.5 billion events from an initial 9×10 10 nuclei, this resulted in just over
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