Calibrating and preserving the energy scale of the tile calorimeter cells during four years of LHC data-taking

TileCal is the hadronic calorimeter covering the most central region of ATLAS experiment at the LHC. This sampling calorimeter uses iron plates as absorber and plastic scintillating tiles as the active material. Scintillation light produced in the tiles is transmitted by wavelength shifting fibers to photomultipliers tubes (PMTs). The resulting electronic signals from the approximatively 10000 PMTs are measured and digitized every 25 ns before being transferred to off-detector data-acquisition systems. A set of calibration systems allow to monitor and equalize the calorimeter at each stage of the signal production, from scintillation light to digitization. This calibration suite is based on signal generation from different sources: A Cs radioactive source, laser light, charge injection and charge integration over thousands of bunch crossings of minimum bias events produced in proton-proton collisions. This contribution presents a brief description of the different TileCal calibration systems and their performances. It elaborates on the methodology of using and combining the individual systems measurements to preserve the calorimeter cell energy scale stable at the % level. The contribution to the LHC luminosity monitoring and measurement is also discussed.