Upgrade of the ATLAS Hadronic Tile Calorimeter for the High Luminosity LHC

The Tile Calorimeter is the hadronic calorimeter covering the central region of the ATLAS detector at the Large Hadron Collider. It is a scintillator-steel sampling calorimeter read out via wavelength shifting fibers coupled to photomultiplier tubes (PMT). The PMT signals are digitized and stored on detector until a trigger is received. The Large Hadron Collider (LHC) has envisaged a series of upgrades towards a High Luminosity LHC (HL-LHC) delivering five times the LHC nominal instantaneous luminosity. The ATLAS Phase II upgrade (2024-2025) will accommodate the upgrade of the detector and data acquisition system for the HL-LHC. In particular, TileCal will undergo a major replacement of its on- and off-detector electronics. In the new architecture, all signals will be digitized and then transferred directly to the off-detector electronics, where the signals will be reconstructed, stored, and sent to the first level of trigger at the rate of 40 MHz. This will provide better precision of the calorimeter signals used by the trigger system and will allow the development of more complex trigger algorithms. Changes to the electronics will also contribute to the reliability and redundancy of the system. Three different front-end options are presently being investigated and will be chosen after studies of simulated physics performance and evaluation of prototype performance in test beams. A hybrid demonstrator compatible with the current ATLAS detector has been developed. The demonstrator is undergoing extensive testing and is planned for future insertion in ATLAS.