The upgrade of the Inner Tracking System of the ALICE experiment

In 2021, for the third run of the CERN Large Hadron Collider(LHC), Pb-Pb collisions will be performed at a centre-of-mass energy per nucleon of 5.5 TeV, with an integrated luminosity of $6×10^{27}cm^{−2}s^{−1}$ and at an unprecedented interaction rate up to 50 kHz. To fulfil the requirements of the ALICE physics program for Run 3, the ALICE experiment at LHC is planning a major upgradeduring the Long Shutdown 2 of LHC in 2019–2020. One of the key elements, is the construction of a new ultra-light and high-resolution Inner Tracking System (ITS) to enhance the determination of the distance of closest approach to the primary vertex,the tracking efficiency at low transverse momenta, and the read-out rate capabilities,with respect to what can be achieved with the current detector. It will consist ofseven layers equipped with silicon Monolithic Active Pixel Sensors (MAPS) witha pixel size of the order of 30×30 $μm^2$ built with the Towerjazz 0.18$μm$ CMOS Imaging process.