# The upgrade of the ALICE Inner Tracking System

## TL;DR

The ALICE Inner Tracking System is being upgraded with advanced silicon pixel detectors to enhance low-momentum particle measurements, improve resolution, and increase readout rate for better heavy-ion collision analysis.

## Contribution

This paper presents the design, development, and production status of the new silicon pixel detector system for the ALICE ITS upgrade, including validation and testing results.

## Key findings

- Successful development of the ALPIDE CMOS MAPS sensor with 5 μm resolution
- Material budget reduced to 0.35% X₀ for inner layers
- Detector modules and staves meet qualification standards

## Abstract

The Inner Tracking System (ITS) of the ALICE experiment will be upgraded during the second long LHC shutdown in $\mathrm{2019}-\mathrm{2020}$. The main goal of the ALICE ITS Upgrade is to enable high precision measurements of low - momentum particles (< 1 GeV/c) by acquiring a large sample of events, benefiting from the increase of the LHC instantaneous luminosity of $\mathrm{Pb}-\mathrm{Pb}$ collisions to $\mathcal{L} = 6 \cdot 10^{27} cm^{-2} s^{-1} $ during Run 3. Working in this direction the ITS upgrade project is focusing on the increase of the readout rate, on the improvement of the impact parameter resolution, as well as on the improvement of the tracking efficiency and the position resolution. The major setup modification is the substitution of the current ITS with seven layers of silicon pixel detectors. The ALPIDE chip, a CMOS Monolithic Active Pixel Sensor (MAPS), was developed for this purpose and offers a spatial resolution of 5 $\mu$m. The use of MAPS together with a stringent mechanical design allows for the reduction of the material budget down to 0.35% $X_0$ for the innermost layers and 1% $X_0$ for the outer layers. The detector design was validated during the research and development period through a variety of tests ensuring the proper operation for the full lifetime inside ALICE. The production phase is close to completion with all the new assembled components undergoing different tests that aim to characterize the modules and staves and determine their qualification level. This contribution describes the detector design, the measurements performed during the research and development phase, as well as the production status.