Speaker
Description
The Beryllium Electron Capture in Superconducting Tunnel Junctions (BeEST) experiment searches for sub-MeV heavy neutrino mass eigenstates. High doses of $^7$Be are directly implanted into high-resolution superconducting tunnel junction (STJ) cryogenic sensors, which measure the nuclear recoil energy of the $^7$Li daughters with 1–2 eV energy resolution. If heavy neutrino states exist, transitions to these states would reduce the recoil energy and generate additional low-energy peaks as a distinctive experimental signature. In Phase III, the BeEST collaboration has collected recoil spectra with $^7$Be activities ranging from 10 to 50 Bq per pixel in a 36-pixel array of STJ sensors, achieving unprecedented precision and statistical significance.
In this poster, we present the latest results from Phase III of the BeEST experiment. We will also discuss improved modeling of the Auger electron escape spectrum and the electron shake-up and shake-off components, which provide the basis for setting new constraints on sterile neutrino mixing in the sub-MeV mass range.
The BeEST experiment is supported, in part, by the DOE-SC Office of Nuclear Physics, the Gordon and Betty Moore Foundation, and the European Metrology Programme for Innovation and Research (EMPIR). TRIUMF receives federal funding via a contribution agreement with the National Research Council of Canada. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract No. DE-AC52- 07NA27344