High-Resolution Aluminum STJ Sensors with In-Situ Laser Calibration for the BeEST Sterile Neutrino Search

The BeEST (Beryllium Electron-capture with Superconducting Tunnel junctions) experiment explores beyond-standard-model physics by precisely measuring the 7Li recoil energy from 7Be electron capture. This two-body decay provides a sensitive probe of the existence of ~keV-scale sterile neutrinos. We present the development progress on the latest generation of aluminum-based superconducting tunnel junction (STJ) sensors, optimized for detecting eV-scale nuclear recoils from implanted 7Be atoms. These devices leverage aluminum's lower atomic number and smaller superconducting gap, achieving sufficient energy resolution to operate alongside our existing tantalum-based sensors. In this talk, we present the details of the Al STJ array design and show their performance when exposed to both UV laser pulses and nuclear decay events. This capability marks an important step towards the future Phases of the BeEST experimental campaign.