Probing sub-GeV dark sectors via high energy proton beams at LBNF/DUNE and MiniBooNE

We study the sensitivity to sub-GeV dark sectors of high energy ($\ge 100\mathrm{GeV}$) proton fixed target experiments such as the Main Injector and the future Long-Baseline Neutrino Facility (LBNF). We focus on off-axis detectors since they have been shown to be the ideal location to reduce the neutrino background. We consider MiniBooNE as an off-axis detector for the NuMI facility and a hyphotetical detector for LBNF located 200 m away from the target and 6.5 degrees off-axis. We find that with the existing data, MiniBooNE can explore new regions of the parameter space for leptophobic dark forces in the 100 MeV–few GeV mass range. The dedicated MiniBooNE run in beam dump mode would further improve the reach for even lighter masses. Therefore, MiniBooNE has the potential to be one of the most sensitive probes of leptophobic dark forces for masses between 1 MeV–10 GeV. Hence we encourage MiniBooNE collaboration to perform a DM dedicated analysis of the existing data coming from neutrinos produced at the Main Injector.

Figure 1

Energy profile of a dark matter particle, either a complex scalar $\varphi$ or a Dirac fermion $\psi$, inside MiniBooNE detector located 750 m away from the target and 6.5° off-axis for a benchmark point $m_{Z^{\prime }}=700\mathrm{MeV}$ and $m_{\chi }=10\mathrm{MeV}$ for a proton beam of 120 GeV.

Figure 2

Expected sensitivity (at 90% C.L., 2 d.o.f.) for a fermionic dark matter particle which interacts with quarks via a leptophobic $Z^{\prime }$ in the mass/coupling plane $({\alpha }_B,M_{Z^{\prime }})$, where ${\alpha }_B=g_z^2/(4\pi )$. The solid red line shows the sensitivity for a detector placed at the MiniBooNE/MicroBooNE site. The gray areas are ruled out (by Kaon and $J/\mathrm{\Psi }$ invisible decay searches), while the purple contour represents the projected sensitivity for the MiniBooNE beam dump run [21, 26].