The ATLAS RPC Phase-II upgrade for High Luminosity LHC era

Resistive Plate Chambers (RPC) detectors play a crucial role in triggering events containing muons in the central region of ATLAS. In view of the High Luminosity-LHC program, the existing RPC system, consisting of six independent cylindrical detector layers each providing a full space time localization of hits, is currently undergoing a significant upgrade. In the next few years, 306 triplets of new generation RPCs will be installed in the innermost region of the ATLAS Muon Barrel Spectrometer, increasing from 6 to 9 the number of tracking layers, doubling the trigger lever arm. This allows a substantial enhancement of the present trigger redundancy, increasing the coverage from 76% to approximately 96%. Fitting new chambers in the narrow space left in ATLAS inner barrel was a challenge, achieved by optimizing RPC materials and thickness, featuring a 1 mm gas gap (instead of 2 mm), and 1.4 mm resistive electrodes (instead of 1.8 mm) while reaching an high rate capability. To achieve such results, a 100 ps precise Time-to-Digital Converter (TDC) has been integrated in the front-end electronics ASIC. The expected time resolution of a single 1 mm RPC gas gap is approximately 300 ps, and the possibility of a stand-alone Time of Flight measurement will have a huge impact on ATLAS searches for massive long-lived particles. An overview and the present status of the ATLAS RPC Phase-II project will be presented.