Exploring Portals to a Hidden Sector Through Fixed Targets

TL;DR

This paper investigates how neutrino experiments at fixed target facilities can detect hidden sectors with new neutral particles, especially through vector portals, and shows current experimental constraints on these models.

Contribution

It analyzes the sensitivity of neutrino experiments to hidden sector portals, focusing on the kinetic-mixing vector portal and current experimental constraints.

Findings

LSND, MiniBooNE, and NuMI datasets severely constrain certain hidden sector models.

Neutrino experiments can detect dark matter beams via neutral-current interactions.

LSND provides the strongest direct constraint on MeV-scale dark matter.

Abstract

We discuss the sensitivity of neutrino experiments at the luminosity frontier to generic hidden sectors containing new (sub)-GeV neutral states. The weak interaction of these states with the Standard Model can be efficiently probed through all of the allowed renormalizable `portals' (in the Higgs, vector, and neutrino sectors) at fixed target proton beam facilities, with complementary sensitivity to colliders. We concentrate on the kinetic-mixing vector portal, and show that certain regions of the parameter space for a new secluded U(1) gauge sector with long-lived sub-GeV mass states decaying to Standard Model leptons are already severely constrained by the datasets at LSND, MiniBooNE, and NuMI/MINOS. Furthermore, scenarios in which portals allow access to stable neutral particles, such as MeV-scale dark matter, generally predict that the neutrino beam is accompanied by a `dark matter beam', observable through neutral-current-like interactions in the detector. As a consequence, we show that the LSND electron recoil event sample currently provides the most stringent direct constraint on MeV-scale dark matter models.