Recoil imaging for dark matter, neutrinos, and physics beyond the
  Standard Model
  Recoil imaging entails the detection of spatially resolved ionization tracks
generated by particle interactions. This is a highly sought-after capability in
many classes of detector, with broad applications across particle and
astroparticle physics. However, at low energies, where ionization signatures
are small in size, recoil imaging only seems to be a practical goal for
micro-pattern gas detectors. This white paper outlines the physics case for
recoil imaging, and puts forward a decadal plan to advance towards the
directional detection of low-energy recoils with sensitivity and resolution
close to fundamental performance limits. The science case covered includes: the
discovery of dark matter into the neutrino fog, directional detection of
sub-MeV solar neutrinos, the precision study of coherent-elastic
neutrino-nucleus scattering, the detection of solar axions, the measurement of
the Migdal effect, X-ray polarimetry, and several other applied physics goals.
We also outline the R&D programs necessary to test concepts that are crucial to
advance detector performance towards their fundamental limit: single primary
electron sensitivity with full 3D spatial resolution at the $\sim$100
micron-scale. These advancements include: the use of negative ion drift,
electron counting with high-definition electronic readout, time projection
chambers with optical readout, and the possibility for nuclear recoil tracking
in high-density gases such as argon. We also discuss the readout and
electronics systems needed to scale-up such detectors to the ton-scale and
beyond.
