Development of the ATLAS Event Picking Server

During LHC Run 2, the ATLAS experiment collected almost 20 billion real data events and produced about three times more simulated events. During physics analysis it is often necessary to retrieve one or a few events to inspect their properties in detail and check their reconstruction parameters. Occasionally it is also necessary to select larger samples of events in RAW format to reconstruct them with enhanced code. The new Event Picking Server automates the procedure of finding the location of the events using the EventIndex and submitting the Grid jobs to retrieve the individual events from the files in which they are stored.