The first of a new breed of experiments on neutrinos has detected an energy pattern consistent with earlier hints that those subatomic particles have mass. However, the prevailing theory of particle physics assumes no mass for the three types of neutrinos—electron, muon, or tau neutrinos.
Since 1998, experimenters have found that neutrinos can change types—a process possible only if neutrinos have some mass (SN: 12/14/02, p.