Abstract
The Beryllium Electron capture in Superconducting Tunnel junctions (BeEST) experiment uses superconducting tunnel junction (STJ) sensors, operated below 100 mK, to perform high-resolution recoil spectroscopy of the two-body decay 7Be + e- → 7Li + νe and search for physics beyond the standard model (BSM). In earlier BeEST phases, cooling was provided by wet adiabatic demagnetization refrigerators (ADRs), which reliably achieved operational temperatures, but only in discrete cycles, limiting the time for continuous data acquisition. This constraint reduced data-collection efficiency and required frequent sensor re-tuning between cycles. To overcome these limitations, phase-IV of the BeEST experiment employs a dilution refrigerator that provides continuous cooling to well below 100 mK. We describe the experimental design modifications required for this transition and present results from the in-situ calibration of STJ detectors in a dilution refrigerator environment. These developments pave the way for sustained high-statistics data acquisition and enhanced sensitivity in the BeEST search for new physics.
*"The BeEST experiment is supported, in part, by the DOE-SC Office of Nuclear Physics, the Gordon and Betty Moore Foundation, NSERC (Canada), and EMPIR (Europe). 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. This work is supported by the US Department of Energy, Office of Nuclear Physics and the Laboratory Directed Research and Development Program at the Pacific Northwest National Laboratory, a multiprogram national laboratory operated by Battelle for the US Department of Energy under contract DE-AC05-76RL01830."
