How do you spot a subatomic neutrino in a "haystack" of particles streaming from space? That's the daunting prospect facing physicists studying neutrinos with detectors near Earth's surface. With little to no shielding in such non-subterranean locations, surface-based neutrino detectors, usually searching for neutrinos produced by particle accelerators, are bombarded by cosmic rays—relentless showers of subatomic and nuclear particles produced in Earth's atmosphere by interactions with particles streaming from more-distant cosmic locations. These abundant travelers, mostly muons, create a web of crisscrossing particle tracks that can easily obscure a rare neutrino event.