1. Very Crude Background Estimation Takeyasu Ito Los Alamos National Laboratory

2. 2 Cold neutron beam intensity: 4.3x10 6 /cm 2 /s/A @8.9A – Note: this is a wide beam. Trap volume: 240cc (l=30cm, r=1.6cm) UCN production: 3x10 -3 UCN/cc/s  decay Signal : 0.2 Hz (detection efficiency=31%) Background: 6 Hz  2 Hz (out of which 0.6 Hz is due to activation) – Note: the UCN production rate is significantly (by a factor of ~100) lower compared to the expected UCN production for the EDM for similar beam intensity. This is mainly because of the shallowness of the trap potential (and also because the FNPB beam is polarized). NIST Lifetime Experiment C.R.Brome et al., Phys. Rev. C 63, 055502 (2001); C.R.Brome, PhD thesis

3. 3 Scaling with beam intensity and trap volume FNPB UCN line beam intensity at 8.9A: 4.5x10 6 /cm 2 /s/A EDM measurement cell volume: 8 liters Scaled background due to activation: 0.6 Hz x 8.0L/0.24L x 4.5/4.3 = 3.9 Hz – Note: Since FNPB UCN beam line is monochromatic, this is an overestimate as far as the beam intensity scaling is concerned. – Even if we start with the 6 Hz background for NIST exp, we get 39 Hz. Expected  decay rate: 1.5 kHz Expected n 3 He reaction rate: 2.4 kHz