Designing a Chopper Configuration to Improve the Sensitivity of the nEDM@SNS Experiment

The Baryonic Asymmetry of our Universe has been a source of intrigue for more than fifty years. Unable to reconcile this disparity with the standard model, physicists have sought answers through beyond- standard- model probes. One such measurement is the search for the neutron electric dipole moment (nEDM), which may identify the source of the CP violation needed to satisfy theories seeking to explain the existence of our universe. The nEDM@SNS experiment being conducted at Oak Ridge National Laboratory will use the techniques of Golub and Lamoreaux to measurement the nEDM with unprecedented precision. The measurement is based on the detection of scintillation light created as ultra-cold neutrons (UCNs) are captured on polarized He-3. UCNs are generated by down-scattering neutrons inside a measurement cell containing superfluid He-4. All neutrons coming down the beam line have the potential to scatter inside the measurement cells and produce background processes that obscure our measurements, but only those in a narrow wavelength (energy) slice near 8.9 Angstrom (1.0 meV) will produce the UCNs we need. Choppers periodically block neutron transmission, and we will use them to select only useful neutrons from the total beam. Through use of the McStas ray-tracing software and independent Monte Carlo simulations, we found an ideal setup using a two-chopper configuration making use of the existing Fundamental Physics Beamline chopper drive trains and two new narrow opening wheels rotating at different speeds.