The design and expected performance of the ALICE ITS3 upgrade

TL;DR

The ALICE ITS3 upgrade introduces a novel, low-material, monolithic pixel detector with cylindrical geometry, promising significant improvements in tracking resolution and physics capabilities in the LHC experiment.

Contribution

This paper presents the conceptual design, R&D achievements, and projected performance of the innovative ITS3 detector for ALICE, emphasizing its low material budget and cylindrical architecture.

Findings

Achieved a material budget of 0.09% X0 per layer.

Projected twofold improvement in pointing resolution for low pT particles.

Demonstrated feasibility through successful R&D and finalized design reports.

Abstract

During the LHC Long Shutdown 3 (2026-29) ALICE will replace its three innermost tracking layers by a new detector, the "ITS3". It will be based on newly developed, wafer-scale monolithic active pixel sensors, which are bent into truly cylindrical layers and held in place by light mechanics made from carbon foam. Unprecedented low values of material budget (0.09\% $X_0$ per layer) and proximity to the interaction point (19 mm) lead to a factor two improvement in pointing resolutions for particles from very low $p_{\mathrm{T}}$ (O(100 MeV/$c$)), achieving, for example, 20 $\mu$m and 15 $\mu$m in the transversal and longitudinal directions, respectively, for 1 GeV/$c$ particles. After a successful R&D phase (2019-2023), which demonstrated the feasibility of this innovative detector and led to the Technical Design Report (https://cds.cern.ch/record/2890181/), the final sensor and mechanics are being developed right now. This contribution will review the conceptual design and the main R&D achievements, as well as the current activities and road to completion and installation. It includes a projection of the improved physics performance, in particular for heavy-flavor mesons and baryons, as well as for thermal dielectrons that will come into reach with this new detector installed.