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Abstract |
Coherent elastic neutrino-nucleus scattering (CEuNS) has been experimentally confirmed using neutrinos from pion decay at rest, solar neutrinos, and reactor antineutrinos. Future CEuNS experiments will lead to precision measurements, which will be a powerful tool to search for new physics beyond the standard model. In this work, we investigate possible deviations from unitarity in the 3 & times; 3 leptonic mixing matrix that controls the propagation of active neutrinos. Such deviations may originate from the mixing with additional gauge singlet fermions, and depending on their mass scale and mixing, the resulting phenomenology can differ substantially. We explore two well-motivated regimes: the seesaw limit, where the new fermions are heavy and kinematically inaccessible, leading to effective deviations from unitarity in the active sector, and the light sterile limit, where they are light enough to be produced and participate in neutrino propagation and scattering processes. We show how these scenarios modify both CEuNS and elastic neutrino-electron scattering, and we present the corresponding sensitivity projections for a future CEuNS reactor experiment obtained by upscaling the CONUS+ experiment, which reported the first observation of reactor CEuNS. We identify the leading experimental systematics relevant for such an upscaling and demonstrate the resulting capability to probe TeV-scale new physics. Our results highlight the strong potential of CEuNS to test the structure of the lepton sector and to search for physics beyond the standard model. |
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