Speaker
Description
Precise measurements of electron capture (EC) decays provide a sensitive probe of physics beyond the Standard Model, as the final state contains a neutrino and a recoiling atom, allowing any new massive particle coupled to the neutrino to be detected through momentum conservation via the nuclear recoil. The Beryllium Electron capture in Superconducting Tunnel Junctions (BeEST) collaboration has pioneered this technique, using $^{7}$Be implanted into tantalum superconducting tunnel junction (STJ) detectors to set world-leading exclusion limits on sterile neutrinos in the mass range of 100-850 keV, and set limits on the spatial width of the neutrino. In this work, the goal is to understand the mechanism driving the broadening of the EC decay spectra of BeEST by investigating an alternative detector technology: the “HVeV” detector, initially developed by the SuperCDMS collaboration for electron-recoil dark matter detection. With demonstrated sub-eV energy resolution, these devices have since been employed in a broader range of measurements relevant to low-mass dark matter searches. HVeV detectors consist of a silicon substrate instrumented with arrays of transition edge sensors (TESs). As phonon-mediated silicon sensors, they provide a complementary study to STJs, enabling studies of how different host materials influence atomic and lattice effects in the EC process. The $^{7}$Be implantation runs were performed at TRIUMF, and the detectors were measured at SLAC. We present the first analysis of $^{7}$Be recoil measurements using HVeV detectors and discuss the application of this technology to precision measurements for neutrino physics.