Performance of the ATLAS Tile Hadronic Calorimeter at LHC in Run I and planned upgrades

The Tile Calorimeter (TileCal) is the central section of the ATLAS hadronic calorimeter at the Large Hadron Collider, a key detector for the measurements of hadrons, jets tau leptons and missing transverse energy. Scintillation light produced in the tiles is transmitted by wavelength shifting fibers to photomultiplier tubes (PMTs). The resulting electronic signals from approximately 10000 PMTs are measured and digitized before being transferred to off-detector data-acquisition systems. After an initial setting of the absolute energy scale in test beams with particles of well-defined momentum, the calibrated scale was transferred to the rest of the detector via the response to radioactive sources. The calibrated scale was validated in situ with muons and single hadrons and the timing performance with muons and jets as detailed in this contribution. The data quality procedures used during the LHC data-taking and the evolution of the detector status are exposed. The energy and the time reconstruction performance of the digitized signals is presented and the noise behavior and its improvement with the detector consolidation in maintenance periods are shown. A set of calibration systems allow the monitoring and the equalization of the calorimeter channels response via signal sources that act at every stage of the signal path, from scintillation light to digitized signal. These partially overlapping systems are described in detail, their individual performance is exposed as well as comparative results on the response evolution of the calorimeter with time during the full LHC data-taking period. The procedure of setting the absolute energy scale for channels/cells is described and the challenge of preserving it at the % level during 3 years of LHC collision data is described. Its main upgrade will occur for the High Luminosity LHC phase (phase 2) where the peak luminosity will increase 5-fold compared to the design luminosity (10³⁴ cm⁻²s⁻¹) but with maintained energy (i.e. 7+7 TeV). An additional increase of the average luminosity with a factor of 2 can be achieved by luminosity leveling. This upgrade will probably happen around 2022. The TileCal upgrade aims at replacing the majority of the on- and off-detector electronics so that all calorimeter signals are directly digitized and sent to the off-detector electronics in the counting room. To achieve the required reliability, redundancy has been introduced at different levels. Three different options are presently being investigated for the front-end electronic upgrade. Which one to use will be decided after extensive test beam studies. 10 Gbps optical links are used to read out all digitized data to the counting room while 5 Gbps down-links are used for synchronization, configuration and detector control. For the off-detector electronics a pre-processor (ROD) is being developed, which takes care of the initial trigger processing while temporarily storing the main data flow in pipeline and de-randomizer memories.