The ALICE Inner Tracker System Upgrade

The phase II upgrade of the Large Hadron Collider (LHC) at CERN is planned under the assumption that the LHC will progressively increase the luminosity of heavy ion beams, eventually reaching an interaction rate of about 50 kHz in Pb-Pb collisions, i.e. instantaneous luminosities of L = 6 × 1027 cm−2s−1. In this perspective, the two main ALICE tracking devices, the TPC and the Inner Tracking system (ITS) will be both upgraded to cope with the foreseen interaction rates. In particular, the various ALICE silicon detectors will be fully replaced with a new, high-resolution, multi-layered, low-material, 12500 megapixel system allowing for very high data rates, and enhancing the vertexing and tracking capabilities at low transverse momenta (pT ). The challenge and the uniqueness of the new ALICE ITS is the very small material budget of the silicon tracker, which will be a factor 4 to 5 smaller than existing similar systems at CERN. The present article describes the design and implementation of complex and reliable assembly procedures (focusing on the detector Outer Layers) which was crucial to push the new ITS technology into production.