A proposal to upgrade the ATLAS RPC system for the High Luminosity LHC

The architecture of the present trigger system in the ATLAS Muon Barrel was designed according to a reference luminosity of 10^34 cm-2 s-1 with a safety factor of 5, with respect to the simulated background rates, now confirmed by LHC Run-1 data. HL-LHC will provide a luminosity 5 times higher and an order of magnitude higher background. As a result, the performance demand increases, while the detector being susceptible to ageing effects. Moreover, the present muon trigger acceptance in the barrel is just above 70%, due to the presence of the barrel toroid structures. This scenario induced the ATLAS muon Collaboration to propose an appropriate upgrade plan, involving both detector and trigger-readout electronics, to guarantee the performance required by the physics program for the 20 years scheduled. This consists in installing a layer of new generation RPCs in the inner barrel, to increase the redundancy, the selectivity, and provide almost full acceptance. The first 10% of the system, corresponding to the edges of the inner barrel even sectors (BIS), has been already approved by ATLAS and will be installed in 2018, to reinforce the trigger in the region between barrel and endcap. To match the performance requirements, the new RPCs will have a different structure, materials and a high performance front-end electronics, in SiGe technology. We will illustrate the performance of the new detectors and trigger system, as well as the impact on the ATLAS physics performance.