Speaker
Description
Solid state photodetectors are broadly used in many areas of research, from high energy physics at colliders to low energy one for solid state studies. The DarkSide collaboration is going to explore a new direction by using large arrays of Silicon Photo Multipliers (SiPMs) for direct dark matter search, where Photo Multiplier Tubes (PMTs) have been used until now. The DarkSide-20k (DS-20k) experiment, currently in construction at Laboratori Nazionali del Gran Sasso (LNGS), will feature a 50 tonnes (20 fiducial) argon-based double-phase TPC (Time Projection Chamber) to probe WIMP-nucleon cross section down to 10$^{-48}$ cm$^2$. The top and the bottom planes of the TPC will be tessellated by 21 m$^2$ (10.5 m$^2$ each) of low-noise SiPM-based detectors with quantum efficiency greater than 40% at 420 nm designed to work at cryogenic temperatures. They will measure the light emitted by scintillation and ionization processes in the two phases of the TPC after a conversion from 128 nm to 420 nm operated by a TPB wavelength shifter. A great effort was carried out by the collaboration to reach an excellent single-photon resolution by selecting radiopure materials whose specific activities reach values down to few mBq/kg. The SiPMs themselves were custom developed for DS-20k by Fondazione Bruno Kessler (FBK) in Trento and produced by LFoundry in Avezzano, both of them located in Italy.
The mass production of 528 20 $\times$ 20 cm$^2$ Photo Detection Units (PDUs), composed by 16 $ 5 \times 5 $ cm$^2$ SiPM tiles each, is ongoing in Nuova Officina Assergi (NOA), an ISO-6 cleanroom built at LNGS equipped with production and testing facilities for large-area SiPM matrices. The DS-20k tiles, composed by 24 SiPMs read-out by a single trans impedance preamplifier, are the smallest self-consistent photodetector modules assembled in NOA and their production (more than 10000 tiles in total) represents an unprecedented effort for the INFN research center. The set up of a near-infrared CMOS camera, recently introduced in the NOA facility, enables a much deeper comprehension of our detectors, with the identification of the defective ones. The measurement of the light emission of a biased tile imaged by our CMOS camera demonstrated to be a powerful tool to identify SiPMs with high current leakages. Therefore they can be replaced, allowing the tiles to recover their full functionality. This process sensitively increases NOA’s tile production yield. A further study is ongoing to find a correlation between the light emission properties of SiPMs and the dark count rate of the tiles measured in liquid nitrogen.
| Speaker Confirmation | Yes |
|---|