Do sterile neutrinos—hypothetical particles that do not interact with matter except through gravity—really exist? If so, this would solve some of today’s major mysteries in particle physics and cosmology. For two decades, researchers around the globe have sought evidence that would prove or disprove the reality of sterile neutrinos, with inconclusive outcomes.
Now, a new result has all but ruled out the possible existence of a light sterile neutrino in a regime suggested by an earlier experiment. Researchers from two major international collaborations—the Main Injector Neutrinos Oscillation Search (MINOS) at Fermi National Laboratory and the Daya Bay Reactor Neutrino Experiment in the south of China—joined forces, each contributing years of data that, taken together, paint a nearly complete picture. The joint result published in Physical Review Letters has significantly shrunk the hiding space for a light sterile neutrino.