Design and characterization of the SiPM tracking system of NEXT-DEMO, a demonstrator prototype of the NEXT-100 experiment

Abstract

NEXT-100 experiment aims at searching the neutrinoless double-beta decay of the 136Xe isotope using a TPC filled with a 100 kg of high-pressure gaseous xenon, with 90% isotopic enrichment. The experiment will take place at the Laboratorio Subterr'aneo de Canfranc (LSC), Spain. NEXT-100 uses electroluminescence (EL) technology for energy measurement with a resolution better than 1% FWHM. The gaseous xenon in the TPC additionally allows the tracks of the two beta particles to be recorded, which are expected to have a length of up to 30 cm at 10 bar pressure. The ability to record the topological signature of the ββ0ν events provides a powerful background rejection factor for the ββ experiment.In this paper, we present a novel 3D imaging concept using SiPMscoated with tetraphenyl butadiene (TPB) for the EL read out and itsfirst implementation in NEXT-DEMO, a large-scale prototype of theNEXT-100 experiment. The design and the first characterizationmeasurements of the NEXT-DEMO SiPM tracking system are presented. TheSiPM response uniformity over the tracking plane drawn from its gainmap is shown to be better than 4%. An automated active controlsystem for the stabilization of the SiPMs gain was developed, based onthe voltage supply compensation of the gain drifts. The gain is shownto be stabilized within 0.2% relative variation around its nominalvalue, provided by Hamamatsu, in a temperature range of 10°C.The noise level from the electronics and the SiPM dark noise is shownto lay typically below the level of 10 photoelectrons (pe) in theADC. Hence, a detection threshold at 10 pe is set for the acquisitionof the tracking signals. The ADC full dynamic range (4096 channels) isshown to be adequate for signal levels of up to 200 pe/μs, whichenables recording most of the tracking signals.