Shedding Light on Neutrino Masses with Dark Forces

TL;DR

This paper explores how new dark forces, specifically a B-L gauge symmetry, can enhance the detection of right-handed neutrinos at colliders and beam dump experiments, potentially revealing the origin of light neutrino masses.

Contribution

It analyzes the sensitivity of LHC and SHiP experiments to displaced RHN decays mediated by a B-L gauge force, linking experimental reach to neutrino mass parameters.

Findings

Experiments can probe neutrino parameters responsible for SM neutrino masses.

Sensitivity depends on the square of the B-L gauge coupling.

On-shell mediator production enhances detection prospects.

Abstract

Heavy right-handed neutrinos (RHNs) provide the simplest explanation for the origin of light neutrino masses and mixings. If the RHN masses are 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 such experiments, the RHN decays after traversing a macroscopic distance from the collision point. The experimental sensitivity to RHNs is significantly enhanced if there is a new "dark" gauge force connecting them to the Standard Model (SM), and detection of RHNs 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 the RHNs 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 RHNs, 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.