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S30XL-LESA/LDMX
An effort has been underway for quite some time to determine the baseline calibrations for the SVT readout channels. The goal is to improve on the baselines which were determined during online calibration runs, if possible. Some runs were taken when the online calibrations might have become stale, some high-occupancy channels experience shifts in their baseline due to power-busing on the APV25 chip.
Cameron and Alic initiated this effort soon after the 2019 run with the following outline:
See this presentation for details and results from run 10648.
Since we may wish to incorporate some kind of baseline calibration/monitoring during the upcoming 2021 run, it was decided to investigate whether this could be done as part of the online Data Quality Management (DQM). This would involve filling the requisite histograms as part of the DQM stream and fitting the plots as part of the endOfData() method. Depending on the memory requirements, this could be accomplished as part of the normal DQM processing, or could be split off into a separate process.
During the data-accumulation phase, a 2D histogram is created for each sensor. The x axis corresponds to the strip / readout channel number and the y axis contains the value of the first of the six APV25 readout channels. The split-strip thin sensors in layers one and two contain 512 strips, while the remaining sensors have 640 strips.
During the endOfData() phase, every y slice of each histogram is analyzed. If there are sufficient entries in the slice a peak-finding algorithm is run to identify the baseline peak. If the peak structure is well-behaved a Gaussian function is fit to the bins in the peak. If this algorithm fails, a second algorithm is run to handle special cases. The results are then plotted and the next slice / histogram is processed.
A prototype Driver has been written, histograms have been created for all 295 "good" runs, and run 10648 has been processed in order to compare with the earlier analysis.
The output histograms with their fits can be found in this pdf file. The plots fall into five categories:
The vast majority of the 20096 channels were successfully fit and the fits appear to capture the peak position of the baseline although, as Alic has shown, it's not always clear what the baseline position should be. Inspection of these plots by SVT experts is welcomed and feedback would be appreciated, especially for the channels for which no fit is currently done.
The online baseline runs will be processed to provide a double-check on the expected means and widths.
The remaining 294 of the "good" runs from 2019 will be processed. It is to be expected that some further algorithm development will be needed to handle new edge cases or to tweak the few parameters in the current code.
Once this has been accomplished and quality assurance metrics have been identified the channel baselines (corresponding to the mean of the Gaussian fit) can be written out in such a manner that they can be uploaded to the database.