The TESSERACT project is currently in a planning phase, funded under the DOE Dark Matter New Initiatives program, and aims to produce fully defined experiments (dubbed HeRALD and SPICE) that will explore DM mass parameter space down to 10 MeV, with upgrade paths to sub-MeV. It will be sensitive to both nuclear recoil DM
(NRDM) and electron recoil (ERDM). An initial period of targeted R&D is needed to make technical choices
and retire technical risks, leading to a well-defined set of design parameters with baseline values.
Multiple target materials will be used, sharing identical readout. In addition to maximizing sensitivity
to a variety of DM interactions, this provides an independent handle on instrumental backgrounds. The
HeRALD experiment will use superfluid helium as a target material. Helium, with its light mass, has good
NRDM sensitivity, but minimal sensitivity to low-mass dark photons. The SPICE experiment will use polar
crystals, which will ultimately have the best sensitivity to dark photon mediated DM, but require lower
energy thresholds than LHe for the same NRDM reach. Scintillating crystals such as GaAs have sensitivity
to ERDM with kinetic energy greater than the electronic bandgap of the material.