Fast Interaction Trigger for ALICE upgrade

We present the structure, functionalities and the first in-beam performance of the ALICE Fast Interaction Trigger (FIT). FIT comprises three detectors: FT0, FV0 and FDD, which use Cherenkov and scintillation effects to detect charged particles originating from proton–proton (pp) and heavy-ion collisions. FIT generates triggers for ALICE, monitors luminosity and background, measures collision time, and determines global collision parameters, such as forward multiplicity, centrality and event plane. FIT uses dedicated front-end electronics to measure time and charge of pulses at pp bunch crossing interval of 25 ns and pp (Pb–Pb) interaction rates of up to 1 MHz (50 kHz). FIT has been installed in ALICE, and its commissioning is ongoing. Upon exposition to pp collisions at the LHC injection energy of $E_{CMS}$ = 450 GeV FIT shows good performance in terms of the collision time resolution of 26 ps and the vertex resolution of 0.8 cm. It is important to note that the presented figures reflect the performance of non-calibrated detectors at lower-than-nominal collision energy (13–14 TeV). They are, therefore, expected to improve.