The NUCLEUS experiment

NUCLEUS is a cryogenic experiment to search for the coherent elastic scattering of Neutrinos on the nucleus (CEnNS). The study of this process offers a unique way to investigate neutrino properties and to search for new physics beyond the Standard Model. Nuclear reactors are promising sources to explore this process at low energies since they produce large fluxes of anti-neutrinos with typical energies of a few MeV. The Nucleus experiment is a Collaboration of institutions from Germany, France, Italy and Austria. The first phase of the experiment will use cryogenic detectors which feature an unprecedentedly low energy threshold and a time response fast enough to be operated in aboveground. The experiment will be placed inside the CHOOZ reactor complex in France, at a distance of 72 m and 102 m from the two 4.25 GWth cores. The site, called “Very Near Site (VNS)”, is an excellent opportunity for the experiment as it allows for a short baseline from the neutrino source. The main aim of the first phase is the measurement of the CEnNS cross section with 20% precision in less than one year of data taking, foreseen in 2022. A second phase of the Nucleus experiment is also foreseen in order to improve the precision on the CEnNS cross-section down to 1% and to start testing New Physics. The challenges for the second phase are the increase of the target size and the reduction of the uncertainty on the neutrino flux and spectrum.

Sketch of the Chooz nuclear power plant and of the Very-Near-Site (VNS)

Sketch of the NUCLEUS experiment at the VNS. The setup consists of a cryostat (1), where the target detectors are installed in its lower part, the experimental volume (2). The latter is surrounded by a passive shielding (3) consisting of alternating layers of borated PE and lead. The top part will be completed by a cold shield inside the cryostat. The outermost layer is the active muon-veto (4) made from plastic scintillator panels. The full setup with a footprint of approximately 1m2 is placed on a weight support platform (5). Further support structures, e.g. for the cryostat, are omitted for clarity. The schematics shows an example setup of a multi-layer passive shielding.