The ATLAS Tile Calorimeter Performance and Its Upgrade towards the High-Luminosity LHC

The Tile Calorimeter (TileCal) is a sampling hadronic calorimeter covering the central region of the ATLAS experiment. TileCal uses steel as absorber and plastic scintillators as active medium. The scintillators are read-out by the wavelength shifting fibres coupled to the photomultiplier tubes (PMTs). The analogue signals from the PMTs are amplified, shaped, digitized by sampling the signal every 25 ns. Each stage of the signal production is monitored and calibrated to better than $1\%$ using multistage calibration systems. The performance of the calorimeter has been measured and monitored using calibration data, cosmic ray muons and the large sample of proton–proton collisions acquired during LHC Run II. The high-luminosity phase of LHC, delivering five times the LHC nominal instantaneous luminosity, is expected to begin in 2027. TileCal will require new electronics to meet the requirements of a 1 MHz trigger, higher ambient radiation, and to ensure better performance under high pileup conditions. Changes to the electronics will also contribute to the data integrity and reliability of the system. New electronics prototypes were tested in laboratories as well as in beam tests. Results of the calorimeter calibration and performance during LHC Run II are summarized, the main features and beam test results obtained with the new front-end electronics are also presented.