SiPM-matrix readout of two-phase argon detectors using electroluminescence in the visible and near infrared range

Abstract

Proportional electroluminescence (EL) in noble gases is used in two-phase detectors for dark matter searches to record (in the gas phase) the ionization signal induced by particle scattering in the liquid phase. The “standard” EL mechanism is considered to be due to noble gas excimer emission in the vacuum ultraviolet (VUV). In addition, there are two alternative mechanisms, producing light in the visible and near infrared (NIR) ranges. The first is due to bremsstrahlung of electrons scattered on neutral atoms (“neutral bremsstrahlung”, NBrS). The second, responsible for electron avalanche scintillation in the NIR at higher electric fields, is due to transitions between excited atomic states. In this work, we have for the first time demonstrated two alternative techniques of the optical readout of two-phase argon detectors, in the visible and NIR range, using a silicon photomultiplier matrix and electroluminescence due to either neutral bremsstrahlung or avalanche scintillation. The amplitude yield and position resolution were measured for these readout techniques, which allowed to assess the detection threshold for electron and nuclear recoils in two-phase argon detectors for dark matter searches. To the best of our knowledge, this is the first practical application of the NBrS effect in detection science.

Review of Liquid Argon Detector Technologies in the Neutrino Sector

“…Optical readout of dual-phase LArTPCs offers an alternative approach to the existing and previously described charge readout methodology. As noted previously in Section 3, Townsend multiplication occurring in the THGEM/LEM holes not only produces additional electrons, but also secondary scintillation light (hereafter denoted by "S2"), and studies have shown that-depending on the exact amplification field across the THGEM/LEMmany hundreds of S2 photons can be produced for every drift electron [85][86][87][88][89]. Optical readout therefore relates to the detection of these S2 photons.…”

“…Although there are a wide variety of photo-sensitive detectors available with which to observe the S2 light, one of the key requirements for use in a neutrino detector must be the capability for high resolution tracking and position reconstruction, as previously noted in Section 3. With this in mind, in recent years devices such as commercial SiPMs [85,89] and CCDs ("charge-coupled devices") [90] have been used to optically read out smallscale dual-phase LArTPCs, and linearly graded SiPMs ("LG-SiPMs") have also shown potential following initial tests conducted in a gaseous TPC [91]. (LG-SiPMs are a relatively new type of SiPM that natively produces 3D position information using a combination of 2D microcell sensor structure and nanosecond timing resolution [92].)…”

Neutral bremsstrahlung and excimer electroluminescence in noble gases and its relevance to two-phase dark matter detectors

“…4 Photon emission spectra in gaseous Ar due to excimer scintillations in the VUV measured in [15], NBrS EL at 8.3 Td theoretically calculated in [4] and atomic scintillations in the NIR measured in [16,17]. Also shown is the photon detection efficiency (PDE) of the typical SiPM [18] It has a line emission spectrum [3,16] (see Fig. 4) and a ∼1 Td higher electric field threshold compared to excimer EL, i.e.…”

Performance of the ReD TPC, a novel double-phase LAr detector with silicon photomultiplier readout

“…The ReD TPC shares several key characteristics of the future DarkSide-20k experiment, including some elements of the mechanical design, but on a smaller scale. The main technological advance is a readout system based entirely on SiPMs, which offer the possibility of a higher photon detection efficiency relative to typical cryogenic photomultipliers [4,12,13]. The ReD detector discussed here is the first double-phase argon TPC read out by SiPMs to be stably operated on the time scale of months and fully characterised with neutron and γ sources.…”

“…Fig 13. Measured S1 distribution from a 83m Kr calibration run with E d = 183 V/cm, superimposed with the normalised environmental background and the best fit to a template (Monte Carlo signal + background data) that accounts for detector resolution.…”