Abstract At the Deep Underground Neutrino Experiment (DUNE). a proton beam hits a fixed target leading to large production rates of mesons. These mesons can decay and potentially provide a source of long-lived neutral fermions. Examples of such long-lived fermions are heavy neutral leptons which can mix with the standard-model active neutrinos. https://www.marcelovicente.com/product-category/smoothing-balm-to-streighten-and-protect/