Towards sub-eV nuclear recoils, a new probe for new physics

I will describe ongoing R&D which aims to open up a new experimental frontier:  atomic recoils at eV and meV energies.  Motivations for these technologies include testing low-mass (keV-MeV mass) dark matter models, and searching for electromagnetic(-like) neutrino interactions such as a magnetic moment.  Nuclear recoils at this energy disperse their energy in the form of phonons in the surrounding material, and typically ONLY phonons.  From a detector standpoint, we are entering the ‘phonon-only regime’.  I will focus on two technologies.  First I will introduce a detector in which the target material is superfluid 4He at mK temperatures.  This material is special in several respects, including the ‘quantum evaporation’ signal channel in which a single phonon at the liquid surface liberates a single atom into the vacuum.  Second, I will describe several new neutron sources for calibrating detector response in this regime.