A High-Granularity Timing Detector for the Phase-II upgrade of the ATLAS Calorimeter system: Detector concept description and first beam test results

The expected increase of the particle flux at the high luminosity phase of the LHC(HL-LHC) with instantaneous luminosities up to 7.5·10$^{34}$cm$^{−2}$s$^{−1}$ will have a severe impact on the ATLAS detector performance. The pile-up is expected to increase on average to 200 interactions perbunch crossing. The reconstruction performance for electrons, photons as well as jets and transversemissing energy will be severely degraded in the end-cap and forward region. A High GranularityTiming Detector (HGTD) is proposed in front of the liquid Argon end-cap and forward calorimeters for pile-up mitigation. This device should cover the pseudo-rapidity range of 2.4 to about 4.0. Low Gain Avalanche Detectors (LGAD) technology has been chosen as it provides an internal gain good enough to reach large signal over noise ratio needed for excellent time resolution. The requirements and overall specifications of the High Granular Timing Detector at the HL-LHC will be presented aswell as the conceptual design of its mechanics and electronics. Beam test results and measurements of irradiated LGAD silicon sensors, such as gain and timing resolution, will be shown.