# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 2 Single-Phase Experiments
### LArIat  
Due to their location and operation on a neutrino beam, the three LArTPCs in the SBN Program are designed to observe the signal from such a beam--that is, neutrino interactions. However, it is equally important to be able to identify and characterise the backgrounds to that signal: non-neutrino particle interactions that produce the same, or similar, detectable products. For example, charged-current \(\
u_{e}\) elastic scattering results in an electron-induced electromagnetic shower, but a gamma-induced shower can be produced by the decay of a \(\pi^{0}\) into a \(\gamma\) pair followed by one of the \(\gamma\)'s undergoing pair production. LArTPCs are potentially capable of distinguishing between electron- and gamma-induced showers through reconstruction of any pre-vertex tracks (which should be present in electron-induced showers, but not in gamma-induced ones), and measurement of the total deposited energy (which should be twice as high for the gamma-induced \(e^{+}e^{-}\) pair than for the single \(e^{-}\) that initiates the electron-induced shower). The ArgoNeuT experiment produced the first (and currently only) exploration of shower separation in a LArTPC, using a small dataset [39]. The Liquid Argon In A Testbeam (LArIAT) experiment [40], located at the Fermilab Test Beam Facility, aims to further that investigation using higher statistics, as well as perform precision measurements of other charged particle LAr interactions--not just to better understand their role as background to neutrino interactions, but also because they are naturally scientifically interesting in their own right. LArIAT operated with various hardware configurations between 2015 and 2017 [40], but the basic detector design remained the same throughout. The cryostat, which was inherited from ArgoNeuT and is shown in Figure 17, is a cylindrical double-walled design, with the space between the inner and outer walls acting as a vacuum jacket for heat insulation. The TPC is situated within the inner vessel. The two ends of the cryostat, which are referred to as \"upstream\" (the end through which the beam enters the detector) and \"downstream\" (through which the beam exits), are sealed by inner and outer convex end-caps. A thin titanium beam window has been added to the outer upstream end-cap, and the inner upstream end-cap has been modified with the addition of a hollow volume  
Figure 16: A model of one of the SBND photon detection system (PDS) box assemblies, containing 5 8-inch diameter Hamamatsu PMTs and eight X-ARAPUCA (“Argon R&D Advanced Program at UniCAmp”) devices. The central PMT is uncoated, and the rest are coated with TPB. These assemblies are installed behind the wire planes of the APAs. Depending on the exact location, some of the X-ARAPUACs are replaced by ARAPUACs, and/or coated with TPB [34]. Taken from [33]. referred to as the \"excluder\" [40]. Together, the beam window and excluder significantly reduce the amount of uninstrumented material that the beam encounters before entering the active LAr within the drift volume. The LAr purification and recirculation system at LArIAT is based on the system developed at the Liquid Argon Purity Demonstrator [41]. That facility demonstrated that it is possible to achieve extremely high LAr purity, and therefore long electron lifetimes (exceeding 6 ms), without first having to evacuate the containing vessel to vacuum. This is particularly important for detectors which use membrane cryostats (such as the previously discussed SBND, as well as the ProtoDUNE detectors and the future DUNE LArTPCs), as this type of vessel is not capable of holding an internal vacuum. The LArIAT system is capable of reducing impurities to the level of 100 ppt [40], resulting in electron drift times of several milliseconds. The LArIAT drift volume is rectangular, with dimensions of 47 \(\times\) 40 \(\times\) 90 cm [40], giving an active LAr mass of 237 kg. The cathode is positioned on the left side of the TPC when viewed from the upstream end.