Speaker
Description
The Inner Tracking System (ITS2) plays a crucial role in tracking and vertex reconstruction in the ALICE experiment at Large Hadron Collider (LHC). The detector consists of seven cylindrical layers equipped with Monolithic Active Pixel Sensors (MAPS), featuring a pixel size of 27 by 29 $\mu$m and sensor thickness of 50-100 $\mu$m. Since the beginning of Run 3 in August 2022, ITS2 has demonstrated stable operation at interaction rates up to 4 MHz in pp and 50 kHz in Pb--Pb collisions, having recorded more than 82 pb$^{-1}$ proton--proton events at $\sqrt{s}$ = 13.6 TeV and 3 nb$^{-1}$ PbPb events at $\sqrt{s_{\rm{NN}}}$ = 5.36 TeV.
In preparation for the LHC Long Shutdown 3 (2026-2029), the ALICE collaboration is developing ITS3, which will replace the three innermost layers of ITS2. This innovative upgrade employs stitching technology in 65 nm CMOS MAPS to produce large-area sensors (approximately 10 x 26 cm$^{2}$). The ultra-thin sensors (50 $\mu$m) can be bent into a half-cylindrical shape, enabling a simplified mechanical structure with only six silicon sensors and light carbon forms. This design achieves a remarkable material budget of 0.07\% X$_{0}$ per layer and reduces the innermost layer radius to 19 mm, projecting a factor of two improvement in tracking performance at low transverse momentum.
This talk will introduce the operational experience and performance of the current ITS2, followed by the design and structure of ITS3, including recent R\&D activities, achievements and expected physics performance improvements.
