Ionization-based search for magnetic monopoles using the NOvA Far Detector

Abstract

We report a search for highly-ionizing magnetic monopoles in the cosmic-ray flux using a 2,713-day dataset collected during 2015--2025 with the NOvA Far Detector, a 14-kiloton segmented detector located on the Earth&#39;s surface in Minnesota, United States. The search is sensitive to monopoles across a wide range of speeds, $7 \times 10^{-4} < β< 0.995$, and is sensitive to masses as low as $2 \times 10^5~\mathrm{GeV}$ for the fastest monopoles. No signal was observed. With the detector&#39;s large surface area and minimal overburden, we achieve the strongest flux limits reported to date in several regions of speed and mass. For heavy monopoles with masses above $10^{13}$ GeV that are able to reach the detector from above or -- crossing the Earth -- from below, we find a flux limit $ϕ_{90\%} < 2 \times 10^{-16}\, \mathrm{ cm^{-2} s^{-1} sr^{-1}}$ (90\% C.L.) for monopoles with $0.005 < β< 0.8$. Across the same range of speeds, we report a limit ${ϕ_{90\%}} < 8 \times 10^{-16}\, \mathrm{ cm^{-2} s^{-1} sr^{-1}}$ for light monopoles with masses above $10^8$ GeV that can reach the detector from above.