Speaker
Description
ITS3 - A truly cylindrical tracker for ALICE
Anna Villani on behalf of the ALICE Collaboration
The ALICE experiment at the CERN Large Hadron Collider (LHC) is optimized for the study of the strongly interacting state of matter arising in high-energy heavy-ion collisions through the tracking of particles at high multiplicities resulting from the collisions. The ALICE Inner Tracking System (ITS) is responsible for primary and secondary vertex reconstruction and particle tracking in the vicinity of the interaction point.
The ALICE ITS will be upgraded during LHC Long Shutdown 3 (2026-2030). The three innermost layers of the current ITS2 will be replaced by a truly cylindrical tracker, the ITS3. Such a vertex detector will comprise three layers, each composed of two self-supporting, ultra-thin (≤50 µm) flexible and bent Monolithic Active Pixel silicon Sensors (MAPS) covering a large area (O(10×27 cm$^2$)). The radius of the first layer of 19 mm and the unprecedented low material budget of 0.09 %X/X0 per layer will strongly improve the pointing resolution especially for low-momentum particles. An improvement of a factor of 2 is foreseen for particles with a p$_T$ lower than 1 GeV/c , thus allowing for the increase in the precision of measurements in the heavy-flavour sector and bringing another set of fundamental observables into reach: the measurement of B$^0_s$ and Λ$^0_b$ at low transverse momenta and of non-prompt D$^+_s$ and Ξ$^+_c$ decays in heavy-ion collisions will be possible.
The final sensor for the ITS3 will be a stitched wafer-scale MAPS sensor realised using a 65 nm CMOS imaging process. The sensor technology has been validated through characterisation both in the laboratory and with in-beam measurements of pixel test structures. First stitched prototypes called MOnolithic Stitched Sensor (MOSS) and MOnolithic Stitched sensor with Timing (MOST) were produced to prove the stitching principle, assess the yield and the performance of wafer-scale sensors. The design of the final full-function sensor prototype (MOSAIX) is underway.
Mechanical and electrical properties of prototypes, which were bent to the ITS3 required radii, were demonstrated to be maintained after bending. Cooling efficiency and mechanical stability of engineering models employing dummy silicon and heating elements were verified under an airflow of 8 m/s, demonstrating a large margin with respect to the requirements. The development of the readout system and the services is well advanced.
This contribution will provide an overview of the ITS3 upgrade project and the results from the qualification campaign on sensor prototypes, mechanics design and detector integration.
| Workshop topics | Detector systems |
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