Commissioning Module Occupancy

The plot below shows the initial occupancy and - chip offset vs chip number for data run 004 for the commissioning module. The algorithm used to calculate the chip thresholds for this run was

Thresh = offset + 3 * offset dispersion + 4 * noise

where offset, offset dispersion, and noise were determined on a chip by chip basis. The plot clearly shows an anti-correlation between the occupancy and the chip offset. This suggests that the chip offsets, determined from three threshold scans at different charge injection values, are not the real offsets for the chips. The real chip-to-chip offsets probably have a much smaller spread than what is found from the linearity fits.