Advances in Stanford phonon-mediated elementary particle detectors

Abstract

We have demonstrated a new phonon sensor design based on aluminum phonon collection pads connected to tungsten transition-edge sensors (TES). The device is patterned onto a silicon crystal and phonons produced by events in the Si are absorbed into the aluminum films where about half of the energy is converted into long-lived quasiparticle excitations. These diffuse until they encounter the lower gap W regions where they deposit their potential energy to the electron system in the W. With the Si crystal at ∼ 40 mK, the W is kept near the center of its resistive transition ( ∼ 90 mK) using voltage bias and Joule self-heating. Current changes induced by particle events are measured with a high-bandwidth SQUID amplifier readout. We have demonstrated an energy resolution of ∼ 360 eV FWHM and a position sensitivity of ∼ 0.2 mm for 55Fe X-rays. We have also completed a new analysis of the nuclear recoil versus electron recoil ballistic phonon production experiments which used our earlier generation Ti TES on Si crystals. The new results set an upper limit on the distinction between the two phonon spectra and provide a better understanding of the phonon sensor response.