Speaker
Description
During Long Shutdown 3 (LS3, scheduled 2026-2029) a new Inner Tracking System (ITS) will be installed in ALICE for the future Run 4 data taking. At present, the ALICE ITS is at its second version, ITS2, formed by 7 layers of silicon CMOS Monolithic Active Pixel Sensors (MAPS). The 3 innermost layers are collectively referred to as Inner Barrel (IB), while the outermost ones form the Outer Barrel (OB). Each layer is then divided along the azimuthal direction into staves of ALPIDE (ALICE PIxel DEtectors) chips, and cooled by a water system.
The future ITS upgrade to ITS3, after LS3, will see a dramatic change in the IB structure, through a replacement of the ITS2 layers with innovative bent large-scale stitched sensors, produced with the TPSCo 65 nm technology. Each of the ITS2 IB layers will be replaced by 2 of these sensors, bent into truly half-cylindrical shapes. Sensor bending allows to reduce the need for mechanical frame support: this innovation, in addition to the replacement of water cooling with air cooling, is expected to thin out the material budget down from an average 0.36% X$_{0}$ to 0.09% X$_{0}$ per layer. The upgrade will also see a reduction of minimum radial distance from the beam axis from 23 to 19 mm, an improved granularity of 20×22.5 μm$^{2}$ and a wider pseudo-rapidity range, up to |η| ≤ 2.5 for the innermost layer. Compared to ITS2, the new ITS3 will also have to withstand larger radiation loads, a maximum limit of which has been estimated at 10$^{13}$ 1 MeV n$_{eq}$cm$^{-2}$ NIEL and 10 kGy TID.
This contribution will present an overview of the ALICE ITS3 upgrade project goals and innovations, as well as the R&D process results and achievements: TPSCo 65 nm technology has been validated by testing the first Multi-Layer Reticle 1 (MLR1) small test devices, both in laboratory and under test beam, even at larger NIEL levels than the ITS3 goal. For the yield and stitching assessment part of ITS3 R&D, current test results of ITS3 stitched devices from Engineering Run 1 (ER1) will also be shown. Finally, we will give a hint to the design of MOSAIX, the latest ITS3 stitched sensor prototypes, currently awaiting submission.
