  We have developed a contact-less technique for the real time measurement of
a-thermal (Cooper-pair breaking) phonons in an absorber held at sub-Kelvin
temperatures. In particular, a thin-film aluminum superconducting resonator was
realized on a 30-grams high-resistivity silicon crystal. The lumped-element
resonator is inductively excited/read-out by a radio-frequency microstrip
feed-line deposited on another wafer; the sensor, a Kinetic Inductance Detector
(KID), is read-out without any physical contact or wiring to the absorber. The
resonator demonstrates excellent electrical properties, particularly in terms
of its internal quality factor. The detection of alphas and gammas in the
massive absorber is achieved, with an RMS energy resolution of about 1.4 keV,
which is already interesting for particle physics applications. The resolution
of this prototype detector is mainly limited by the low (about 0.3%) conversion
efficiency of deposited energy to superconducting excitations
(quasi-particles). The demonstrated technique can be further optimized, and
used to produce large arrays of a-thermal phonon detectors, for use in rare
events searches such as: dark matter direct detection,neutrino-less double beta
decay, or coherent elastic neutrino-nucleus scattering.
