Inside the Experimental Traps Scientists Set for Ghostly Neutrinos

More than a quarter of a century before, physicists had been puzzling over why energy appeared to be lost during a radioactive process called beta decay. Something was missing, and there was no known physics to explain it. Then in 1930, the Austrian physicist Wolfgang Pauli proposed a radical solution: A virtually undetectable particle was silently carrying the missing energy away. “I have done a terrible thing,” Pauli told a friend. “I have postulated a particle that cannot be detected.” It would come to be known as the neutrino. Having almost no mass and no charge, these particles can pass through Earth and everything on it, including our bodies, virtually unimpeded.