Construction, Commissioning and Performance Measurements of the Inner Tracking System Upgrade (ITS2) of ALICE at the LHC

A Large Ion Collider Experiment (ALICE), situated on the Large Hadron Collider (LHC), is optimised to study relativistic heavy-ion collisions in order to quantitatively characterise the Quark Gluon Plasma. The inner-most detector system, the Inner Tracking System (ITS), is responsible for primary and secondary vertex reconstruction in the vicinity of the interaction point, as well as stand-alone tracking of particles unable to reach the rest of the ALICE sub-detectors, due to momentum cut-off and acceptance limitations. The ITS was upgraded over the LHC Long Shutdown 2 (late 2018 - early 2022) with the aims of improving the impact parameter resolution, tracking efficiency, transverse momentum resolution, and readout rate. This was achieved by replacing the ITS used in LHC Runs 1 and 2 by seven concentric layers of silicon pixel detector, utilising a Monolithic Active Pixel Sensors (MAPS) design known as ALPIDE, together with the reduction of the radius of the inner-most layer by 16 mm, the reduction of the material budget and the decrease of the pixel pitch. Over the last few years, the upgraded ITS, ITS2, was successfully constructed at several international sites before being assembled into the concentric barrel structure of the final tracker at CERN. The detector was then integrated into the final services including the readout and power systems before undergoing a comprehensive commissioning campaign. This thesis concerns the construction, characterisation, and commissioning of the outer-most four layers of the ITS2, known as the Outer Barrel. Namely, the construction and characterisation of the detector modules and staves, the verification of the final system, and the acquisition of the first real particle data set and subsequent performance measurements.