The REINFORCE project engages and supports citizens to cooperate with researchers and actively contribute to the development of new knowledge for the needs of science and society. The aim is to bridge the gap between them, and reinforce society’s science capital. Within this context, the demonstrator “New Particle Search at CERN” will engage citizen-scientists in searches for new elementary particles in the high-energy proton-proton collisions at the LHC. To make this possible, the demonstrator adopts a three-stage architecture. The first two stages use simulated data from the ATLAS detector to train citizens, but also to allow for a quantitative assessment of their performance and comparison with machine learning algorithms. The third stage uses real data from the ATLAS Open-Data subset, providing two research paths: (a) study of Higgs boson decays to two photons, one of which could be converted to an electron-positron pair, and (b) search for yet undiscovered long-lived particles predicted by certain theories Beyond the Standard Model.