Test of the performances of Alice’s chip at BTF

It’s now come to an end the BTF (Beam Test Facility) measurements campaign for the characterization of one of the most innovative silicon pixel chips that will be used by the ALICE experiment for the new tracker detector.

The building of a new ITS (Inner Tracking System) entirely based on silicon pixel detectors, made up of 7 concentric layers, for a total active surface of about 10 m² of segmented silicon and more than 12.5 billion pixels, greatly involves the INFN, especially the ALICE group at LNF, which will be one of the five laboratories in the whole world to engage in this particular construction.

Before finalizing the design and starting production, it is obviously essential to check and validate the correct operation of the detector; for this reason, a group of researchers from the ITS project, in collaboration with the BTF colleagues, tested 6 prototypes, checking the excellent characteristics of the detectors, for example, in terms of detecting efficiency.

More than 1000 different working positions of the detectors were tested experimentally, gathering data that is essential to determine the best option, among those available, for the final detector in terms of geometry of the collecting anode or reset mechanism. This data will allow the finalization of the design of the sensor and the start of the production, a fundamental step for the whole project.

A long and fruitful R&D phase assured this result, thanks to the INFN fundamental contribution, together with a chip, pALPIDE-3, whose final dimensions (1.5×3 cm²) are segmented in half a million pixel measuring 28×28 µm². This was fabricated using the TowerJazz MAPS (Monolithic Active Pixel Sensor) technology and is provided with all the required features.

This would not have been possible, in such a short time, without the BTF characteristics, especially its ability to radiate the chip uniformly, despite its dimensions, and to adapt the electron flux to optimize the collecting statistics.