Search for ultralight dark matter in the SuperMAG high-fidelity dataset

Ultralight dark matter, such as kinetically mixed dark-photon dark matter (DPDM) or axion-like-particle dark matter (axion DM), can source an oscillating magnetic-field signal at Earth's surface. Previous work searched for this signal in a publicly available dataset of global magnetometer measurements maintained by the SuperMAG collaboration. This "low-fidelity" dataset reported measurements with a 1-min time resolution, allowing the search to set leading direct constraints on DPDM and axion DM with Compton frequencies f(DM) <= 1/(1 min) (corresponding to masses m(DM) <= 7 x 10(-17) eV). More recently, a dedicated experiment undertaken by the SNIPE Hunt collaboration has also searched for this same signal at higher frequencies f(DM) >= 0.5 Hz (or m(DM) >= 2 x 10(-1)5 eV). In this work, we search for this signal of ultralight DM in the SuperMAG "high-fidelity" dataset, which features a 1-sec time resolution, allowing us to probe the gap in parameter space between the low-fidelity dataset and the SNIPE Hunt experiment. The high-fidelity dataset exhibits lower geomagnetic noise than the low-fidelity dataset and features more data than the SNIPE Hunt experiment, making it a powerful probe of ultralight DM. Our search finds no robust DPDM or axion DM candidates. We set constraints on DPDM and axion DM parameter space for 10(-3) Hz <= fDM <= 0.98 Hz (or 4 x 10(-18) eV <= mDM <= 4 x 10(-15) eV). Our results are the leading direct constraints on both DPDM and axion DM in this mass range, and our DPDM constraint surpasses the leading astrophysical constraint in a narrow range around m(A ') approximate to 2 x 10(-15) eV.