In order to obtain the beam polarizations at the point of collision (Interaction Point = IP), we have two polarimeters located 1,800 m in front of and 150 m behind the IP. The question is: will the polarization at the IP be the same we measure with the polarimeters?

On the way between the polarimeters, there are quite a few magnets whose fields rotate the spin of the beam particles due to their magnetic moment. For a particle following the reference orbit, it is possible to place the magnets such that the polarization will be the same at all three points of interest (the polarimeters and the IP). However, a beam is not point-like and not all magnetic fields are homogeneous. Thus, particles which are a little way off the reference orbit will experience different fields with different effects on their spins. Furthermore, the magnets cannot be positioned with arbitrary precision. Displaced magnets will have the same effect as a shift of the beam position with regard to the reference orbit. Finally, the collision with the other beam will also affect the polarization measured at the downstream polarimeter.

All those effects are way too complex to compute their influences on the polarization analytically. Therefore, a comprehensive simulation is set up to investigate how precisely we can know the polarization at the IP from our measurements.