(Presented 23 Apr 2012 at C&A)
I tried to search for the reason of unexpected variation of CAL response vs energy noticed by Carmelo
while he compared p7 reprocessed data with existing data:
Quick look at CREs with Pass7 full reprocessing.
During original processing we used 2 MevPerDAC calibration files:
- fit_protonCalib_calibOps_17runs.calMPD.xml
- based on data collected Jul15, 2008
- used to process data in August - October, 2008
- fit_protonCalib_nomoSciOps_week26sep3oct2008_sum_try2.calMPD.xml
- based on data collected Sep 26 - Oct 3, 2008
- used to process all data since November 2008
For pass7 reprocessing we used 17 new MPD calibration files each based on 6 Ms of data and used to reprocess data for the same period
Following plot shows the evolution of average ratio of calibration coefficients for HE and LE diodes with time for old calibration files (red points) and new calibration files (blue points).
All values on the plot are divided by 53.15 (actual mean ratio of MeVPerDAC coefficients of HE and LE diodes).
This plot confirms that the use of first calibration file with lower HE/LE ratio until October 2008 should introduce 0.8 % drop of energy response at high energies. Qualitatively this is consistent with effect found by Carmelo, but has magnitude lower by factor of 2. This is still to be understood.
Average pedestal drift in HEX8 range between July and October 2008 is ~0.5 MeV and cannot explain such change in HE/LE diode ratio.