The primary purpose of this step is to refine the time based tracking calibration. Specifically, the calibration constants for the time to distance function need to be calibrated and checked. This involves choosing calibration runs evenly spaced throughout the running period and the processing of at least 100K events from each of those runs. The exact frequency by which runs should be calibrated depends on the running period. Obviously, if the calibration constants change by a large amount from one calibration run to another the frequency of updating calibrations should be increased. A rule of thumb is the tracking calibrations should be checked at least once for every day of the running period.
While the primary purpose of this step is to obtain a first set of time based tracking calibrations, this step also provides a good opportunity to assess the overall quality of all calibrations. An early assessment of the quality of all calibration allows one to direct resources in an efficient manner by identifying potential problems early on in the cooking process. During this step all of the monitoring and batch submission machinery developed for production processing of the data is used to process 100K event in each tracking calibration run. Single particle yields, cross sections, tracking figures of merit, and calibration constants can all be examined as a function of run number. Problematic running periods can be identified, and runs can be selected for the next stage of analysis. In addition, this step is early enough in the cooking process to allow for modification of the software to account for novel running conditions.