Data Analysis - Overview

Calibration and Passes

Overview

The XEM2 analysis can be broken into two major parts; online and offline data-taking. Online data-taking leverages the online GUI, and the 50k replays. These will be discussed below. Timing windows and reference times must be set for each trigger type that will be used in an experiment. Additionally, for online analysis 'okay' calibrations need to be 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.

The offline analysis is comprised of all the same steps, but the level of detail is increased to understand the systematic uncertainties, optimal calibration parameters, cut quantities. This process typically takes several iterations as detector calibrations depend on one another in some cases. For instance, the drift chambers are used to construct tracks, which can be used in the calorimeter calibration code to sum energy deposition in clusters of blocks around projected electron hits. Most importantly, the hodoscope needs to be properly calibrated for almost all detector calibrations.

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.

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.