The Online Luminosity Calculator of ATLAS

Online luminosity monitoring at the LHC is important for optimizing the luminosity at the experimental insertions and vital for good data taking of the LHC experiments. It is an important diagnostic tool, in particular for the normalization of trigger rates and data samples. The ATLAS experiment has several sub-detectors, which can be used for relative luminosity measurements. In order to collect all data from the variety of different sources and to process them centrally, the software application “Online Luminosity Calculator” has been developed. It is written in C++ and integrated into the ATLAS online software framework. There are three main tasks of this application: first, collection of data from the sub-detectors and the LHC beam instrumentation. This requires handling of online information published in various formats, using different middleware. Further, calibration of the raw luminosity information, time integration and normalization. The last step is the publication of the results in a coherent format for online usage and permanent storage in the conditions database. This contribution will give an overview of the basic concepts of the Online Luminosity Calculator which plays a key role in the luminosity dataflow of ATLAS. Experience and results from the first months of proton collisions will be presented.