Exploring Portals to a Hidden Sector Through Fixed Targets

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.

Figures (3)

• Figure 1: Sensitivity of LSND to decays $V\rightarrow e^+e^-$. The light, medium, and dark shaded regions indicate more than 10, 1000, and $10^6$ expected events respectively. The left panel shows events due to vectors arising from $\pi^0\rightarrow \gamma V$ decays, while the right panel shows events arising from $\Delta(1232)\rightarrow N V$.
• Figure 2: On the left we show the Higgs$'$ decay length $c \tau$ for $\kappa=10^{-2}$ and $\alpha'=\alpha$. The regions are $c \tau<1$m (white), 1 - $10^3$m (light), $10^3-10^6$m (medium), and $> 10^6$m (dark). On the right, we show the sensitivity of LSND ($\pi^0 \to \gamma V h'$ - dark), MiniBooNE ($\rho,\omega \to h'V$ - light), MiniBooNE ($\rho,\omega \to h'V$, muon events only - medium), and MINOS (QCD $\to Vh'$, muon events only - medium), indicating more than 10 events expected in the detector.
• Figure 3: Expected number of neutral current like electron events induced by MeV-scale dark matter scatterings in the LSND detector. We show regions with greater than 10 (light), 1000 (medium), and $10^6$ (dark) expected events. Regions below the black line correspond to a strong coupling regime, with values of $\alpha'> 4\pi$.