Data Analysis - Overview
Calibration and Passes
Overview
The XEM2 analysis can be broken into two major parts; online and offline data analysis.
Online data analysis leverages the online GUI, and the 50k replays. These are used as a quick diagnostic that all detector components are reading out data as expected. For online analysis 'okay' calibrations are made for the hodoscopes, calorimeter, drift chamber, and noble gas cherenkov detectors. These calibration coefficients typically roll over from the previous experiment and are determined using cosmic ray scans and/or early commissioning beam. These become the 'default' calibrations that are overwritten once more in-depth calibrations are done in the offline analysis.
Offline data analysis is a deep dive into the calibrations of each detector for each kinematic and trigger settings. We are moving from 'okay' calibrations for all settings to the best possible calibrations we can have for each kinematic. This is accomplished through many passes through the data where incremental improvements, calibrations / corrections are made.
The first step is to pick the real physics signal. This is done by placing appropriate reference time and timing window cuts. Refer to the reference time and timing window section[1] for more details. Timing windows and reference times must be set for each trigger type that will be used in an experiment. Next, the hodoscope is calibrated. This is typically done once for each experiment / trigger setting. The hodoscope calibration doesn't change much over time. It is mainly checked at this stage once for each kinematic.
Next, the PID detectors are gain matched. That is, software gain coefficients are applied to correct for any differences in high-voltage setting for the PMTs. This is done by following the instructions for calorimeter and Cherenkov calibration. In the case of the SHMS, special delta scan and defocused run was done to ensure there were enough events in each block to do the calibration. The analysis is generally broken up into passes. In each pass, a specific set of calibrations and corrections are applied and the data is replayed. Each set of data in a pass is typically saved to /cache/ to save for comparisons between passes.
Once all the calibrations are completed, systematic checks are performed on efficiencies and live-times. Luminosity scans are performed for the cryogenic targets and pion and charge-symmetric backgrounds are studied.
Carlos Yero made an amazing analysis note based on his thesis experiment, which can be accessed by logging into the private Hall C DocDB and searching for entry 1032.
Hodoscope Calibration
More details found in specific calibration section.
Drift Chamber Calibration
More details found in specific calibration section.
Noble Gas Cherenkov Calibration
More details found in specific calibration section.
Heavy Gas Cherenkov Calibration
Not really used for our analysis
Calorimeter Calibration
More details found in specific calibration section.
