Upgrade of the ALICE Inner Tracking System

TL;DR

The paper discusses the upgrade of the ALICE Inner Tracking System with a new seven-layer Monolithic Active Pixel Sensor detector, significantly enhancing tracking, vertexing, and readout capabilities for high-luminosity heavy ion collisions.

Contribution

It presents the design, R&D, and prototype results of the new Monolithic Active Pixel Sensors for the upgraded ALICE Inner Tracking System.

Findings

Successful development of large-scale pixel sensor prototypes.

Achievement of low material budget suitable for inner detector layers.

Sensors meet radiation and hit density requirements.

Abstract

During the Long Shutdown 2 of the LHC in 2018/2019, the ALICE experiment plans the installation of a novel Inner Tracking System. It will replace the current six layer detector system with a seven layer detector using Monolithic Active Pixel Sensors. The upgraded Inner Tracking System will have significantly improved tracking and vertexing capabilities, as well as readout rate to cope with the expected increased Pb-Pb luminosity of the LHC. The choice of Monolithic Active Pixel Sensors has been driven by the specific requirements of ALICE as a heavy ion experiment dealing with rare processes at low transverse momenta. This leads to stringent requirements on the material budget of 0.3$% X/X_{0}$ per layer for the three innermost layers. Furthermore, the detector will see large hit densities of $\sim 19 \mathrm{cm}^{-2}/\mathrm{event}$ on average for minimum-bias events in the inner most layer and has to stand moderate radiation loads of 700 kRad TID and $1\times 10^{13}$ 1 MeV n$_\mathrm{eq}/\mathrm{cm}^{2}$ NIEL at maximum. The Monolithic Active Pixel Sensor detectors are manufactured using the TowerJazz 0.18 $\mu$m CMOS Imaging Sensor process on wafers with a high-resistivity epitaxial layer. This contribution summarises the recent R&D activities and focuses on results on the large-scale pixel sensor prototypes.