Beijing Electron Spectrometer (BES)
Analysis concerning the beam position
To make use of the vertex information to increase the tracking
position, we need to know the beam positon. We plotted the
distance of closest approach xi versus phi to obtain the
beam position
We calculated xi as the z component of n x p where n is the
normal vector (cos phi,sin phi) and p the positon of closest
approach. So xi=px*sin phi-py*cos phi. We find the beam at
xi=3mm and phi=90 degrees, that is, the beam is displaced from
the origin along the y-axis by 3 mm.
Plot 1 shows a scatter plot of xi versus phi
Plot 2 shows the average xi for a fixed phi.
