  In this white paper, we outline some of the scientific opportunities and
challenges related to detection and reconstruction of low-energy (less than 100
MeV) signatures in liquid argon time-projection chamber (LArTPC) detectors. Key
takeaways are summarized as follows. 1) LArTPCs have unique sensitivity to a
range of physics and astrophysics signatures via detection of event features at
and below the few tens of MeV range. 2) Low-energy signatures are an integral
part of GeV-scale accelerator neutrino interaction final states, and their
reconstruction can enhance the oscillation physics sensitivities of LArTPC
experiments. 3) BSM signals from accelerator and natural sources also generate
diverse signatures in the low-energy range, and reconstruction of these
signatures can increase the breadth of BSM scenarios accessible in LArTPC-based
searches. 4) Neutrino interaction cross sections and other nuclear physics
processes in argon relevant to sub-hundred-MeV LArTPC signatures are poorly
understood. Improved theory and experimental measurements are needed. Pion
decay-at-rest sources and charged particle and neutron test beams are ideal
facilities for experimentally improving this understanding. 5) There are
specific calibration needs in the low-energy range, as well as specific needs
for control and understanding of radiological and cosmogenic backgrounds. 6)
Novel ideas for future LArTPC technology that enhance low-energy capabilities
should be explored. These include novel charge enhancement and readout systems,
enhanced photon detection, low radioactivity argon, and xenon doping. 7)
Low-energy signatures, whether steady-state or part of a supernova burst or
larger GeV-scale event topology, have specific triggering, DAQ and
reconstruction requirements that must be addressed outside the scope of
conventional GeV-scale data collection and analysis pathways.
