Shedding light on neutrino masses with dark forces

Heavy right-handed neutrinos, n , provide the simplest explanation for the origin of light neutrino masses and mixings. if m n is at or below the weak scale, direct experimental discovery of these states is possible at accelerator experiments such as the lhc or new dedicated beam dump experiments; in these experiments, n decays after traversing a macroscopic distance from the collision point. the experimental sensitivity to right-handed neutrinos is significantly enhanced if there is a new “dark” gauge force connecting them to the standard model (sm), and detection of n can be the primary discovery mode for the new dark force itself. we take the well-motivated example of a b − l gauge symmetry and analyze the sensitivity to displaced decays of n produced via the new gauge interaction in two experiments: the lhc and the proposed ship beam dump experiment. in the most favorable case in which the mediator can be produced on-shell and decays to right handed neutrinos (pp → x + v b−l → x + n n ), the sensitivity reach is controlled by the square of the b − l gauge coupling. we demonstrate that these experiments could access neutrino parameters responsible for the observed sm neutrino masses and mixings in the most straightforward implementation of the see-saw mechanism.