...
The plot below shows the trending of pedestal difference with respect to official pre-launch pedestal file for all LEX8 channels over 44 runs:
Similar plot for all HEX8 channels:
The reason for this pedestal drift is higher temperature on orbit with respect to cold_TVAC. Pedestals for the first 12 runs demonstrate some evolution, while CAL temperature was increasing and after that became stable. The maximum pedestal drift is 30 adc units, which corresponds to 1 MeV in LEX8 range and 60 MeV in HEX8 range. It is not very big bias for energy measuremet, but it strongly affects the position measurement along the crystal as the 1% bias of the signal at one crystal end leads to the 5 mm bias in position. This effect is the biggest in HEX8 range starting at 1 GeV, so 60 MeV bias means 6% leading to 3 cm position bias.
...
/nfs/slac/g/svac/chehtman/calibGenCAL_analysis/flight/ped/calPed_28jun08.xml
produced genMuonPed application of calibGenCAL package revision calibGenCAL-05-06-00 from calibOps run 236323982 collected on Jun 28,2008.
Validation of new pedestal file
Anders Borgland has reprocessed 10K events from the run 236323982. The
...
following plot shows the sum of pedestal histograms for all LEX8 channels.
The sigma of the distribution 5.4 adc units matchs exactly the width of individual pedestal (see red histogram below).
...