Speaker
Description
During LHC Long Shutdown 3, the ALICE Experiment will replace its innermost tracking layers with a novel, truly cylindrical pixel tracker (ITS3). The detector will consist of three layers of low power ($40\, \mathrm{mW/cm}^2$) Monolithic Active Pixel Sensors (MAPS) thinned to the point of flexibility ($50\,\mathrm{\mu m}$). By bending these sensors into half-cylinders around the beam pipe, the design gains inherent mechanical stability; this enables the use of air cooling and a minimal mechanical support structure of carbon foam, reducing the material budget to an unprecedented value of approximately $0.09\%\,\mathrm{X_0}$ per layer.
To achieve this, stitched, wafer-scale sensors for each half-layer were developed. The sensors feature between 30 and 50 million pixels ($20.8\,\times\,22.8\,\mathrm{\mu m^2}$), a length of 26.6 cm and a width of up to 9.8 cm, covering 180 degrees of the azimuth and the full longitudinal extent of the tracking layers. The final prototype sensor, MOSAIX, features 12 "repeated sensor units" interconnecting common power and data transmission lines by stitching on silicon, which in traditional detector designs are added externally, again reducing material budget.
Initial tests of the MOSAIX Engineering Run 2 (ER2), conducted both at the wafer level and on bonded chips, show very promising results regarding both the yield of the stitched sensors and their core functionality. A comprehensive testing program is currently underway to verify the full chip functionality and characterise its efficiency, spatial resolution, and radiation hardness. Concurrently, the mechanical integration procedures are being qualified using full-scale engineering models with bent silicon. This presentation provides an overview of the ITS3 project, details the MOSAIX architecture, and reports on the latest performance results and integration progress.