Validation of the New Small Wheel MicroMegas sectors for the spectrometer of the ATLAS experiment at CERN

The inner forward part of the ATLAS muon spectrometer has been substituted by new detectors able to work with excellent performances at the final design luminosity of 7.5 $\times$ 10$^{34}$ cm$^{-2}$ s$^{-1}$ foreseen for the HL-LHC phase. MicroMegas detectors (MM, MICRO MEsh GASeous structure chambers) have been chosen for the New Small Wheel (NSW) muon tracking since they are Micro-Pattern Gaseous Detectors, designed to provide excellent resolution and efficiency, even in a highly irradiated environment. Before being mounted on the mechanical structure, each MM sector is characterized and tested at CERN in terms of high voltage stability and tracking efficiency. Results are presented and some dedicated studies on performances are shown.