Exploring coherent neutrino-nucleus scattering with gram-scale cryogenic calorimeters

Project Information

NU-CLEUS

Grant agreement ID: 804228

DOI

10.3030/804228

Project closed

EC signature date 10 December 2018

Start date 1 April 2019

End date 31 January 2026

Funded under

• EXCELLENT SCIENCE - European Research Council (ERC)

Total cost

€ 1 642 500,00

EU contribution

€ 1 642 500,00

Coordinated by

TECHNISCHE UNIVERSITAET MUENCHEN
Germany

Periodic Reporting for period 4 - NU-CLEUS (Exploring coherent neutrino-nucleus scattering with gram-scale cryogenic calorimeters)

Reporting period: 2023-10-01 to 2025-03-31

Summary of the context and overall objectives of the project

Coherent neutrino-nucleus scattering (CEvNS) is moving frontiers in low-energy neutrino physics.The NUCLEUS reactor-neutrino experiment, which uses cryogenic detectors with energy threshold of a few 10's of eV to detect CEvNS, will serve as a touchstone to search for new physics beyond current knowledge. CEvNS is a weak neutral-current process that has been first proposed in the 1970's as part of the Standard Model of Particle Physics (SM). This new interaction channel opens up a new chapter in neutrino physics. It will address important open questions concerning the interaction and the nature of neutrinos, and has the potential to discover new physics beyond the SM. Further, the technological advances might lead to interesting applications for nuclear non-proliferation. In the framework of project NU-CLEUS the required detector technology has been demonstrated: The world-best energy threshold for nuclear recoils of 19.7+-0.8eV has been achieved with the NUCLEUS detectors, which are single crystals (Al2O3, CaWO4) with a mass of about 1g. The detectors are operated as cryogenic detector at mK temperatures equipped with transition-edge-sensors, a technology that has been pioneered by the CRESST experiment.
In the ERC project NU-CLEUS there is a strong focus on the development and commissioning of the NUCLEUS10g detector at TUM, which is expected to be installed at the nuclear power plant in CHOOZ, France, in 2023. Based on the successful ERC StG application we have built up an international collaboration consisting of about 50 members with significant additional resources for the project. PI Strauss is the spokesperson of the NUCLEUS collaboration. The significantly increased manpower allows to achieve the scientific goals in a competitive manner, such that the experiment is on track to be the first experiment observing CEvNS at reactors.

Work performed from the beginning of the project to the end of the period covered by the report and main results achieved so far

The TUM team has achieved the following milestones for project NU-CLEUS: the procurement, installation and successful commissioning of the dry dilution refrigerator which was funded as major equipment within the grant. The necessary base temperature of <7mK and cooling power have been demonstrated. The fully functional cryostat is the key tool to develop the NUCLEUS10g detector. Furthermore the installation and commissioning of a SQUID readout system for the cryogenic detectors has been demonstrated with 8-channel prototype system. Thereby the necessary noise level has been verified. As the core activities of the team, the NUCLEUS10g detector module has been designed, developed and verified. The detector concept has been worked out in details, including the design of the transition-edge-sensors for the target crystals, the production of the target detector arrays, the cryogenic inner veto detectors, the electronic and thermal connections and an LED calibration devices. Coordinated by TUM, the first two NUCLEUS10g detector modules have been successfully assembled and have passed thermal cycling tests in the new cryostat. All sub-systems of the NUCLEUS10g detectors have been validated. The complete commissioning of the detector modules is planned before summer 2022. To reject harmful vibrations induced by environmental noise and pulse-tube coolers, the development of a novel spring decoupling system for the cryogenic detectors has been performed. The dedicated experimental space at TUM is fully prepared and available to project NU-CLEUS since Dec 2021 for the upcoming blank assembly and commissioning of the NUCLEUS experiment.

Progress beyond the state of the art and expected potential impact (including the socio-economic impact and the wider societal implications of the project so far)

For the remaining funding period of NUCLEUS, the project is on track to achieve its major goal: the first detection of CEvNS at a nuclear reactor. Those are the five milestones until the end of the project:
- Fully commissioning of the NUCLEUS10g detector in the NUCLEUS cryostat
- Installation and commissioning of all NUCLEUS components in the TUM underground laboratory.
- Verification of the detector performance and of the background level.
- Relocation of the full setup to the CHOOZ nuclear power plant.
- Measurement of the CEvNS cross-section with a precision of O(10%).
In parallel, the feasibility of a future upgrade of the detector mass to the kg scale will be investigated, as well as the suitability of the NUCLEUS detector technology for nuclear non-proliferation purposes.