Towards a High Precision Investigation of the Strange Form Factor of the Proton: A Study of the Shift in Detector Signal for Polarized Protons in Matter

Recently, the parity violation present in polarized electron-proton elastic scattering has been used to obtain information about the pairs of virtual strange quarks within the proton. It is thought that a measurement of the corresponding strange form factor at a momentum transfer Q² of 3 (GeV/c)² could be large, a potential discovery. To succeed with such measurements, it is necessary to create a large solid angle detector to track the angular correlation between scattered electrons and recoil-protons. The current proposal suggests the use of calorimeters, and requires detector efficiency to be independent of the electron beam polarization. However, the polarization of the recoil-protons induces a spatial shift in detector signal due to spin-dependent interactions within the calorimeter. If the shift is too large, the cuts made in data analysis cease to be polarization independent. We found using Geant4 that such a shift is approximately 16±1 μm (statistical), which is sufficiently small for the purposes of the proposed experiment. This result allows us to start work on the proposal to the JLab PAC and the design of the experiment.