Hunting the elusive X17 in CEνNS at the ESS

A bstract The so-called X 17 particle has been proposed in order to explain a very significant resonant behaviour (in both the angular separation and invariant mass) of e + e − pairs produced during a nuclear transition of excited 8 Be, 4 He and 12 C nuclei. Fits to the corresponding data point, as most probable explanation, to a spin-1 object, which is protophobic and has a mass of approximately 16.7 MeV, which then makes the X 17 potentially observable in Coherent Elastic neutrino ( ν ) Nucleus Scattering (CE ν NS) at the European Spallation Source (ESS). By adopting as theoretical framework a minimal extension of the Standard Model (SM) with a generic U(1) ′ gauge group mixing with the hypercharge one of the latter, which can naturally accommodate the X 17 state compliant with all available measurements from a variety of experiments, we predict that CE ν NS at the ESS will constitute an effective means to probe this hypothesis, even after allowing for the inevitable systematics associated to the performance of the planned detectors therein.