Dark sector searches at neutrino experiments

Despite considerable progress in the understanding of fundamental particles and interactions and the striking predictive power of the Standard Model in collider experiments, some key questions in the understanding of Nature still remain unanswered. What is the origin of neutrino masses? What is dark matter made of? Why is there an imbalance between baryons and anti-baryons in the Universe? These questions call for new physics beyond the Standard Model. For decades, the majority of the experimental effort has been directed to the search for new particles with sizeable couplings to the Standard Model and masses at the TeV scale. However, recent theoretical and experimental developments have brought new attention to the dark sectors, i.e. extensions of the Standard Model at scales below the electroweak scale and which are weakly coupled to the visible sector. In some of these rich dark sector models, it is possible to have dark photons decaying semi-visibly, meaning that the final state contains both visible and invisible particles, making it possible to circumvent current experimental constraints on the masses of the dark photons and mixing with the SM photon. This project will focus on models containing multiple dark fermions, where the lighter of these can be made stable through some additional symmetry that forbids the mixing with active neutrinos, making it a viable dark matter candidate. This model can leave visible signatures in ProtoDUNE detectors, located at CERN. Protons extracted from the CERN Super Proton Synchrotron (SPS), with energies up to 400 GeV, can generate a flux of BSM particles that can reach the ProtoDUNE detectors. These are liquid Argon Time Projection Chambers (LArTPCs) constructed to test and consolidate the technologies of the DUNE Far Detector. Thanks to its large volume and the high density of liquid argon, stable particles coming into the detector can interact, leading to an excess of electron recoil.