A High-Granularity Timing Detector for the Phase-II upgrade of the ATLAS Calorimeter system: detector concept, description and R&D and firstbeam test results

The expected increase of the particle flux at the high luminosity phase of the LHC (HL-LHC) will have a severe impact on the ATLAS detector performance, especially on jet reconstruction performance in the forward region. A High Granularity Timing Detector is proposed in front of the Liquid Argon end-cap calorimeters for pile-up mitigation and for bunch per bunch luminosity measurements. The aim is to provide a precision timing information for minimum ionizing particle with a resolution better than 50 ps. This detector should cover the pseudo-rapidity range of 2.4 to about 4.0 and be made of two layers per side of Low Gain Avalanche Detectors with 1.3 x 1.3 mm2 pads. The requirements and overall specifications of this detector will be presented as well as the conceptual design and R&D results.