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

We report a search for highly ionizing magnetic monopoles in the cosmic-ray flux using a 2713-day dataset collected during 2015–2025 with the NOvA Far Detector, a 14-kt segmented detector located on Earth’s surface in Minnesota, United States. The search is sensitive to monopoles across a wide range of speeds, 7 × 10 − 4 < β < 0.995 , and is sensitive to masses as low as 2 × 10 5     GeV for the fastest monopoles. No signal was observed. With the detector’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 Earth—from below, we find a flux limit ϕ 90 % < 2 × 10 − 16     cm − 2   s − 1   sr − 1 (90% confidence level) for monopoles with 0.005 < β < 0.8 . Across the same range of speeds, we report a limit ϕ 90 % < 8 × 10 − 16     cm − 2   s − 1   sr − 1 for light monopoles with masses above 10 8     GeV that can reach the detector from above.