Computing strategy for PID calibration samples for LHCb Run 2

The samples for the calibration of the Particle Identification (PID) are sets of data collected by LHCb where decay candidates have a kinematic structure which allows unambiguous identification of one the daughters with a selection strategy not relying on its PID-related variables. PID calibration samples are used in a data-driven technique to measure the efficiency of selection requirements on PID variables in many LHCb analyses. Since the second run of the LHCb experiment, PID variable are computed as part of the software trigger and then refined in the offline reconstruction (this includes two different applications, named Brunel and DaVinci). Physics analyses rely on selections combining PID requirements on the online and offline versions of the PID variables. Because of the large, but not full, correlation between online and offline PID variables, the PID samples must be built such that it is possible to access, particle by particle, both versions of the full PID information, such that combined requirements on the offline and online versions can be defined. The only viable solution is to write the PID Calibration samples to a dedicated stream where the information evaluated in the trigger (the online version) is stored together with the full raw event, which is then reconstructed and processed offline. A dedicated algorithm allows to match online and offline candidates and to produce datasets to be used as input for the package that allows analysts to access the calibration samples. This note is focused on PID Calibration samples, but the general layout should be applied to any other calibration sample in Run 2.