A new Data format for the commissioning phase of the ATLAS detector

In the commissioning phase of the ATLAS experiment, low-level Event Summary Data (ESD) are analyzed to evaluate the performance of the individual subdetectors, the performance of the reconstruction and particle identification algorithms, and obtain calibration coefficients. In the GRID model of distributed analysis, these data must be distributed to Tier-1 and Tier-2 sites before they can be analyzed. However, the large size of ESD (≅1 MByte/event) constrains the amount of data that can be distributed on the GRID and be made readily available on disks. In order to overcome this constraint and make the data fully available, new data formats - collectively called Derived Physics Data (DPD) in ATLAS - have been designed. Each DPD format contains a subset of the ESD data, tailored to specific needs of the subdetector and object reconstruction and identification performance groups. Filtering algorithms perform a selection based on physics contents and trigger response, further reducing the data volume. Thanks to these techniques, the total volume of DPD to be distributed on the GRID amounts to 20% of the initial ESD data. An evolution of the tools developed in this context will serve to produce another set of DPDs that are specifically tailored for physics analysis