The MAPS-based ITS Upgrade for ALICE

Abstract

The Inner Tracking System (ITS) Upgrade for the ALICE experiment at LHC is the first large-area ($\sim$10 m$^2$) silicon vertex detector based on the CMOS Monolithic Active Pixel Sensor (MAPS) technology, which combines sensitive volume and front-end readout logic in the same piece of silicon. This technology allows a reduced material budget (target value of 0.3\% on the innermost layers) thanks to the thin sensors (50-100 $\mu$m) and limited need of cooling, in combination with light-material interconnection circuits and support structures. The small pixel pitch ($\sim$30 $\mu$m), the location of the layers (7 cylindrical layers with radii ranging from 2.3 cm to 39.3 cm from the beam interaction line), and the limited material budget will provide the ALICE experiment with extremely precise tracking resolution. The high-rate readout capabilities will also enable ALICE to collect a large data sample at the 50 kHz Pb--Pb collision rate expected in the LHC Run 3. The new ITS, now assembled at the surface, is currently undergoing an exhaustive pre-commissioning phase with standalone calibration and cosmic ray data-taking, which will be completed by April 2020 before the installation in the ALICE detector. Experience gained from the construction and the pre-commissioning phase, and plans for the installation and preparation for the data-taking in ALICE will be presented in this paper. The role played by the new ITS within the development path of the MAPS technology for future applications will also be briefly discussed.