Next-Generation Tracking System for Future Hadron Colliders

Abstract

The design of future high-energy and high-intensity hadronic machines, such as FCC-hh, relies on the ability of detectors to sustain harsh radiation environments while keeping excellent performances on tracking and tagging all the interaction products. In order to face the challenge, a vast R&D effort is required. In this paper, we propose a novel concept of tracking system, that combines the possibility to track particles up to fluences of the order of 10$^{17}$ n$_{eq}$/cm$^2$ together with a precise time information, $\sigma_t \sim$ 10 ps. For this purpose, Low-Gain Avalanche Diodes (LGAD) are the suited technology. For the innermost, most irradiated portion of the detector, very thin sensors (20 – 40 $\mu$m) with moderate gain ($\sim$ 5 – 10) can provide the required tolerance to the radiation. For such detectors, the internal gain mechanism of LGAD allows to provide the same amount of charge released by a particle passing 100 – 200 $\mu$m of standard PiN diodes up to $\Phi \sim$ 0.5$\cdot 10^{16}$ n$_{eq}$/cm$^2$. Above those fluences, the thin doped layer responsible for the signal multiplication gets deactivated, but if operated at the proper bias voltage ($\sim$ 500 V) the signal multiplication happens inside the whole irradiated bulk volume. Moreover, in the region of the tracker detector where the level of overall fluence keeps $\leq$ 0.5 – 1$\cdot 10^{16}$ n$_{eq}$/cm$^2$, LGAD with a geometry optimised for timing measurement, the so-called Ultra-Fast Silicon Detectors (UFSD), can be used to provide precise position and timing information at the same time. Considering the current timing performances of UFSD under irradiation and assuming a $\sigma_t \sim$ 40 ps from sensor + ASIC, the usage of track-timing layers alternated to tracking only layers can provide an ultimate $\sigma_t \sim$ 10 ps per single track.