The upgrade of the ALICE Inner Tracking System

ALICE is a general purpose experiment dedicated to the study of nucleus-nucleus collisions at LHC. After more than 3 years of successful operation, an upgrade of the apparatus during the second long shutdown of LHC (LS2) in 2017/18 is in preparation. One of the major goals of the proposed upgrade is to extend the physics reach for rare probes at low transverse momentum. The reconstruction of the rare probes requires a precise determination of the primary and secondary vertices that is performed in ALICE by the Inner Tracking System (ITS). The present ITS made of 6 layers of three technologies of silicon devices allows, for example, to reconstruct D mesons with the transverse momentum down to similar to 2 GeV/c. Further extension of this range towards lower PT requires the installation of the new ITS consisting of 7 layers of silicon detectors with significantly better single point resolution and reduced material budget. It is expected that the new system will allow to improve the impact parameter resolution by a factor of similar to 3. Moreover, the data rate capability of the upgraded ITS should be significantly improved in order to exploit the full expected LHC lead-lead interaction rate of 50 kHz, almost two orders of magnitude above the present readout rate. The present contribution describes first the requirements for the new ITS followed by the conceptual design of the system and its expected performance. Secondly, an overview of the different R&D activities from the concept towards the final detector is given. (C) 2013 CERN. Published by Elsevier B.V. All rights reserved.