SiPM and readout electronics for the JUNO-TAO Central Detector

The Taishan Antineutrino Observatory (TAO) is a satellite experiment of the Jiangmen Underground Neutrino Observatory (JUNO). TAO consists of a spherical ton-level Gadolinium-doped Liquid Scintillator detector and its main purpose is the precise measurement of the reactor antineutrino spectrum by detection of light produced in v̅e + p⟶ e + + n reaction, as a reference for JUNO. About 4,500 photoelectrons per MeV could be detected by instrumenting the sphere surface (∼10 m2) with state-of-the-art Silicon PhotoMultipliers (SiPMs), resulting in a sub-percent energy resolution. In this work we present the implemented architecture of the readout electronics based on low-noise, high-speed Front-End Boards (FEBs) connected to a 50×50 mm2 SiPM Hamamatsu tile, composed by 32 SiPM elements of 12×6 mm2 each, divided into two independent output channels. The overall 4,024 FEBs will be supplied through eight custom flanges that have to bring in about 1.5 kW. On the same flanges the 8,048 output signal cables are distributed and routed to the Front-End Controllers (FECs), based on Virtex Ultrascale FPGAs, able to manage up to eight 16-channel ADCs, for a total of 128 channels on a single FEC, with a maximum sampling rate of 250 MHz with 12-bit resolution. A dedicated trigger and data-acquisition system will filter and record occurring events, rejecting dark count events. We report the results of the characterization for the pre-production FEBs batch, following the main figures of merit defined for the experiment, showing single photoelectron resolution better than 13% and dynamic range up to 250 photoelectrons.