Speaker
Description
ALICE 3, a next-generation heavy-ion experiment at the LHC, is proposed as part of the Phase IIb upgrades during the fourth long shutdown (LS4), scheduled in 2034-2035, with data taking planned from Run 5. ALICE 3 aims to exploit the full potential of the High-Luminosity LHC as a heavy-ion collider, targeting an integrated luminosity of 35 nb$^{-1}$ in Pb$-$Pb and 18 fb$^{-1}$ in pp collisions. The physics programme will emphasise heavy-flavour dynamics, electromagnetic probes, and precision low-momentum measurements to probe QCD matter across collision systems.
Central to this effort is the silicon vertex and tracking detector, designed to provide a pointing resolution of 10 ${\mu}$m at $p_\textrm{T}$ = 200 MeV/c at midrapidity and to cover a pseudorapidity range of $|\eta| \leq$ 4. It consists of an Inner Tracker and an Outer Tracker, comprising 11 barrel layers (0.5 $\leq r \leq$ 80 cm) and 2 x 12 disks ($|z| \leq$ 350 cm), covering a total area of about 60 m$^2$. Both sub-systems comprise sensors based on CMOS MAPS technology, building on advances made in the ALICE ITS2 (Run 3) and ITS3 upgrade (Run 4). The Inner Tracker is subdivided into the Vertex Detector and the Middle Layers, featuring MAPS with intrinsic position resolution of 2.5 ${\mu}$m and 10 ${\mu}$m, respectively. The Vertex Detector, located inside the beam pipe, comprises three layers with a material budget as low as 0.1$\% X_0$ per layer. Its retractable design allows the innermost layer to be positioned at 0.5 cm from the beam axis, where the sensors are exposed to radiation levels of 1$\times$10$^{16}$ (1 MeV) n$_{eq}$/cm$^2$ and 300 Mrad, as well as hit rates of 100 MHz/cm$^2$. The Middle Layers, surrounding the Vertex Detector outside the beam pipe, consist of four barrel layers and three disks on either side. The Outer Tracker, comprising four barrel layers and six disks on either side, targets a material budget of 1$\% X_0$ per layer and is designed for large-area coverage with modular, industrially scalable production.
This contribution will discuss the core design concepts and highlight key R&D efforts in sensor development, mechanics, integration, and modularisation, toward the Technical Design Reports expected in 2026.
Reference: ALICE Collaboration, "Letter of intent for ALICE 3: A next-generation heavy-ion experiment at the LHC", CERN-LHCC-2022-009, LHCC-I-038, arXiv:2211.02491 [physics.ins-det].
