Overview
The NUCLEUS experiment focuses on investigating coherent elastic neutrino-nucleus scattering (CE$\nu$NS) involving reactor electron antineutrinos. This research describes the development and commissioning of the cryogenic target-detector module designated for the NUCLEUS Technical Run. This module, developed at the Technical University of Munich, integrates four gram-scale calcium tungstate (CaWO$_4$) detectors. Each detector is equipped with two Transition Edge Sensors (TES), resulting in a combined target mass of 6.96 g.
Research Context
The NUCLEUS experiment aims to study CE$\nu$NS, a process involving neutrino-nucleus interactions, using reactor electron antineutrinos. The experimental setup is planned for deployment at the Chooz nuclear power plant located in France. The successful operation of the target-detector system is identified as a key milestone in advancing cryogenic detector technology for reactor-CE$\nu$NS measurements.
Approach
The research involved several key steps for the target-detector module:
- Development: Designing the cryogenic target-detector module.
- Commissioning: Bringing the developed module into an operational state at the Technical University of Munich.
- Integration: Incorporating the four gram-scale CaWO$_4$ detectors, each fitted with two TES, into the module structure.
- Detector Characterization: Evaluating the performance characteristics of the detectors.
- Energy Calibration: Performing X-ray-based energy calibration for the detectors.
The module's operation was tested in conjunction with a surrounding Cryogenic Outer Veto system. This veto system comprises six kilogram-scale germanium (Ge) detectors, intended for background discrimination.
Findings
The developed cryogenic target-detector module demonstrated specific performance metrics:
- The module contains four CaWO$_4$ detectors, each with two TES, providing a total target mass of 6.96 g.
- Across six characterized detectors, a mean baseline resolution of $\overline{\sigma}_{\mathrm{BL}} = (2.79 \pm 0.60)\,\mathrm{eV}$ was achieved.
- The best-performing detector exhibited a baseline resolution of $\sigma_{\mathrm{BL}} = (2.16 \pm 0.02_{\mathrm{stat}})\,\mathrm{eV}$.
- This best-performing detector's resolution surpassed the design goal by a factor of two.
- The achieved resolution for the best detector represents a state-of-the-art result for a cryogenic CaWO$_4$ detector.
- The target detector module was successfully operated simultaneously with the Cryogenic Outer Veto system.
- No measurable cross-talk was observed between the target detector module and the Cryogenic Outer Veto system.
Why This Matters
The successful development and commissioning of this cryogenic target-detector system demonstrate its readiness for the NUCLEUS Technical Run at the Chooz nuclear power plant. This achievement marks a significant step in the development of cryogenic detectors specifically for reactor-CE$\nu$NS measurements.