ALICE Experiment to Install Revolutionary ITS3 Silicon Vertex Detector During LHC Upgrade
The ALICE collaboration at CERN has detailed its ITS3 upgrade, which will replace the three innermost tracking layers of the detector with a novel cylindrical silicon vertex detector during LHC Long Shutdown 3. The upgrade uses Monolithic Active Pixel Sensors fabricated in a 65nm CMOS process, thinned to 50 micrometers and bent into cylinders as small as 19mm in radius, eliminating traditional support structures and flexible printed circuits. The design reduces the material budget to less than 0.09% of a radiation length per layer, significantly improving tracking precision for heavy-ion physics measurements.
The ALICE Inner Tracking System 3 (ITS3) upgrade, described in a new arXiv preprint, represents a major leap in silicon detector technology for high-energy physics. The detector will be the first to use fully cylindrical, wafer-scale Monolithic Active Pixel Sensors (MAPS), fabricated in a 65nm CMOS process and thinned to just 50 micrometers before being bent to radii as small as 19mm. A key enabling technology is wafer-scale stitching, which produces seamless 27cm-long sensors with integrated power and signal distribution, removing the need for flexible printed circuits inside the active detector volume. The combination of ultra-thin sensors, self-supporting cylindrical geometry, and a switch from water to air cooling reduces the material budget to below 0.09% of a radiation length per layer — a critical figure for minimizing unwanted particle scattering that degrades tracking resolution. Full-scale prototypes, designated MOSS and MOST, have validated stitching feasibility, production yield, and radiation hardness, while engineering models have confirmed that air-convection cooling provides adequate thermal management and structural stability. The upgrade is scheduled for installation during LHC Long Shutdown 3 and is expected to substantially enhance ALICE's ability to reconstruct particle vertices close to the interaction point, benefiting studies of quark-gluon plasma and heavy-flavor physics.
What's missing
The preprint does not specify the exact timeline or scheduled dates for LHC Long Shutdown 3, nor does it quantify the expected improvement in tracking impact-parameter resolution relative to the current ITS2 detector. The paper also does not address the total cost of the upgrade program. As a preprint, it has not yet undergone formal peer review.
What different sources said
- arXiv physicsCenter
Overview of the ALICE ITS3 Upgrade
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