Searching for BSM Neutrino Physics with Phase-III of the BeEST Experiment*

The Beryllium Electron-capture in Superconducting Tunnel Junctions (BeEST) experiment aims to detect signatures of heavy neutrino mass eigenstates in the Beryllium-7 (⁷Be) electron capture process. This is achieved by precisely measuring the nuclear recoil energy of the ⁷Li daughter atom following the momentum "kick" from the neutrino using a superconducting tunnel junction (STJ) sensor. In Phase III, the BeEST has expanded to include a 32-pixel array detector and has increased the implanted Be-7 dose. This talk presents the current progress of the BeEST Phase-III. We detail the enhancements in Be-7 implantation techniques and the newly adopted analysis methods designed to minimize systematic errors. We will also discuss the projected sensitivity of Phase III.