# Review of Liquid Argon Detector Technologies in the Neutrino Sector
## 4 Summary and Outlook  
Single- and dual-phase LArTPCs have been, and continue to be, essential tools for the study of neutrinos. Central to all such detectors is the drifting of electrons produced through LAr ionisation due to the passage of charged particles, and the detection of these electrons (either directly or indirectly) in a way that allows both their population and 3D position to be unambiguously determined with high spatial and temporal precision. In the field of single-phase detectors, the most well-established technology for achieving this is wire-based charge readout, generally taking the form of an anode plane assembly consisting of parallel planes of wires orientated so as to produce independent 2D views of particle interactions. These views are then combined to produce full 3D position reconstruction and calorimetric measurements. Many currently and soon-to-be operating single-phase LArTPCs-such as the ICARUS T600, MicroBooNE and SBND experiments of Fermilab's SBN Program and the ProtoDUNE-SP detector at CERN-make use of wire-based charge readout, alongside other proven technologies such as PMTs for observing the prompt LAr scintillation light and cold front-end electronics that can be located within the cryogenic environment, thereby benefiting from reduced noise and readout complexity. New approaches to single-phase LArTPC technology, and even the underlying design of such detectors themselves, are also being actively explored and promoted by a number of groups. These include the use of (X-)ARAPUCA light traps alongside or as an alternative to PMTs, pixelated charge readouts and modular TPCs as pioneered by the ArgonCube collaboration, and Vertical Drift's perforated PCB anodes and vertically orientated drift volume concept. Dual-phase LArTPCs have only recently been given attention in the neutrino sector. However, due to having been used in dark matter searches for a number of years, the general detection principle of the dual-phase concept-multiplication of the drifted electrons using a THGEM/LEM or other micropattern detector located in the gaseous phase, before collection of the electrons on an anode plane-is well proven. The WA105 experiment was central to the initial establishment of dual-phase LArTPCs for neutrino detection, and its larger successor ProtoDUNE-DP aims to build on this work. In addition, the ARIADNE research program is currently investigating an alternative approach to dual-phase LArTPC design-that of optical readout, via the detection of the secondary scintillation light (initially using EMCCDs, and more recently with TPX3-based cameras) that is produced during electron multiplication. The culmination of many decades of LArTPC development and refinement is the DUNE program, which will have at its heart four colossal LArTPCs containing approximately 10,000 tons of active LAr each. At the time of writing, one of these detectors has been confirmed to use the established single-phase wire-based anode plane assembly design, with the remaining three still to be decided upon. However, given the well-proven nature of both the single- and dual-phase concepts, as well as the variety and potential of the many new approaches being explored, it is clear that no matter what technologies are eventually used, LArTPCs will continue to play a critical and indispensable role in the neutrino sector for many years to come. Conceptualization, [PERSON] ([PERSON]) and [PERSON] ([PERSON]); investigation, [PERSON] ([PERSON]) and [PERSON] ([PERSON]); writing, [PERSON] ([PERSON]) and [PERSON] ([PERSON]). All authors have read and agreed to the published version of the manuscript. The authors are supported by European Research Council Grant No. 677927. Not applicable. **Acknowledgments:** The authors would like to thank the reviewers for the time and effort they have taken to respond to this manuscript, as well as their specific and direct feedback. We found the comments and suggestions most helpful. **Conflicts of Interest:** The authors declare no conflict of interest.