The upgrade of the ALICE Inner Tracking System

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 $6 \times 10^{27}$ 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 upgrade during 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). The upgraded ITS will significantly 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 of seven layers equipped with silicon Monolithic Active Pixel Sensors (MAPS) with a pixel size of the order of $30 \times 30 \mu m^2$. They will be produced by Towerjazz with its $0.18 \mu m$ CMOS Imaging process. To transmit (receive) data to (from) the sensors, Flex Printed Circuits (FPCs) will be wire-bonded to the sensors themselves. One of the main physics goals consist in improving the reconstruction capabilities of heavyflavour mesons and baryons. In addition, the new tracking detector will allow us to study lowmass dileptons and low-$p_T$ charmonia at mid-rapidities.