Abstract

The ALICE experiment at the CERN LHC is designed to study the physics of strongly interacting matter, and in particular the properties of the Quark-Gluon Plasma, using proton-proton, proton-nucleus and nucleus-nucleus collisions. The ALICE collaboration is preparing a major upgrade of the experimental apparatus to be installed during the second long LHC shutdown in the years 2019–2020. A key element of the ALICE upgrade is the new, ultra-light, high-resolution Inner Tracking System. With respect to the current detector, the new Inner Tracking System will significantly enhance the pointing resolution, the tracking efficiency at low transverse momenta, and the read-out rate capabilities. This will be obtained by seven concentric detector layers based on a Monolithic Active Pixel Sensor with a pixel pitch of about 30×30 μm2. A key feature of the new Inner Tracking System, which is optimised for high tracking accuracy at low transverse momenta, is the very low mass of the three innermost layers, which feature a material budget of 0.3% X0 per layer. This contribution presents the design goals and layout of the upgraded ALICE Inner Tracking System, summarises the R&D activities focussing on the technical implementation of the main detector components, and the projected detector performance.

Highlights

  • The main goals of the ITS upgrade are to achieve an improved reconstruction of the primary vertex as well as decay vertices originating from heavy-flavour hadrons and an improved performance for the detection of low-pT particles

  • The Total Ionising Dose (TID) irradiation leads to an effective change of charge threshold of the front-end circuitry resulting in a higher fake-hit rate at low ITHR and detection efficiency close to 100 % over the full range

  • The Flexible Printed Circuit (FPC) consists of a polyimide with a low thermal expansion coefficient plus aluminium and copper as conductor for the Inner Barrel (IB) and Outer Barrel (OB), respectively

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Summary

ALICE ITS upgrade

The main goals of the ITS upgrade are to achieve an improved reconstruction of the primary vertex as well as decay vertices originating from heavy-flavour hadrons and an improved performance for the detection of low-pT particles. The design objectives are to improve the impact-parameter resolution by a factor of 3 and 5 in the r φ- and z-coordinate, respectively, at a pT of 500 MeV/c [4]. The tracking efficiency and the pT resolution at low pT will improve. The innermost detector layer will be moved closer to the interaction point from 39 mm to 23 mm. The granularity will be increased by an additional seventh layer and by shrinking the pixel size from currently 50 μm × 425 μm to about 30 μm × 30 μm. All layers of the upgraded ITS will be equipped with pixel sensors. The upgraded ITS is designed such as the removal and insertion will be possible during the yearly shutdown periods for maintenance

Layout and running environment of the upgraded ITS
ALPIDE — the pixel chip for the ALICE ITS upgrade
Mechanics
Sensors
Readout electronics
Findings
Summary and outlook
Full Text
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