Calibration of Tracking Measurements of the MOLLER Experiment

The MOLLER experiment at Jefferson Lab is designed to measure a precise value of the weak charge of the electron through the parity-violating properties of the weak force. It will do this by measuring the helicity-dependent asymmetry of electron-electron weak scattering, which can then be correlated to the weak charge. In order to sort desired events, the experiment will use a magnetic field to select the elastically scattered events of interest. Before this asymmetry measurement takes place, there will be a calibration phase to, amongst other things, look for any minor discrepancies between the actual and ideal magnetic field. The goal of this project was to analyze how coils offset in the radial direction effect the magnetic field, and to use this analysis to make statements about the calibration phase as a whole. This was done using GEANT4 simulation software, which simulated scattered particles through the magnetic field. From the analysis of these simulations, it was found that sieve holes in sectors neighboring the offset coil exhibited clear linear trends. From these trends it was found that changes in final electron position in the azimuth were much stronger compared to final radial position. Non-neighboring holes displayed very minute offsets compared to neighboring ones, indicating that creating a method of describing coil placements is a separable problem. It was also found that hole position and electron energy effect the sensitivity of electrons to the changing magnetic field, and target position was found to have a minimal effect. From this knowledge, tables were constructed displaying the most sensitive holes for each offset coil. With the data and analysis methods developed during this project it will ensure that future study of the MOLLER magnetic field has a good foundation for future work.