The ITS3 detector and physics reach of the LS3 ALICE Upgrade

TL;DR

The LS3 ALICE upgrade introduces the ITS3 detector with innovative monolithic sensors and lightweight mechanics, significantly enhancing tracking resolution and physics capabilities for heavy-flavour and dielectron measurements.

Contribution

This paper presents the design, R&D progress, and expected physics improvements of the novel ITS3 detector for the ALICE experiment during LS3.

Findings

Achieved a twofold improvement in pointing resolution at low $p_T$.

Developed a new bent wafer-scale monolithic pixel sensor technology.

Projected enhanced sensitivity for heavy-flavour and dielectron measurements.

Abstract

During Large Hadron Collider (LHC) Long Shutdown 3 (LS3) (2026-28), the ALICE experiment is replacing its inner-most three tracking layers by a new detector, Inner Tracking System 3. 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 (per layer) and closeness to interaction point (19 mm) lead to a factor two improvement in pointing resolutions from very low $p_\text{T}$ (O(100MeV/$c$)), achieving, for example, 20 ${\mu}$m and 15 ${\mu}$m in the transversal and longitudinal directions, respectively, for 1 GeV/c primary charged pions. After a successful R\&D phase 2019-2023, which demonstrated the feasibility of this innovational detector, the final sensor and mechanics are being developed right now. This contribution will briefly review the conceptual design and the main R&D achievements, as well as the current activities and road to completion and installation. It concludes with a projection of the improved physics performance, in particular for heavy-flavour hadrons, as well as for thermal dielectrons, that will come into reach with this new detector installed.